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International Training Program: “Urban Transport” PROJECT WORK

“Improving Traffic Conditions in San Salvador: Application of the Swedish Traffic Conflicts Technique. “ Saul Castelar Transportation Engineer El Salvador scastelar@yahoo.com

April 2007

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Contents

Introduction ........................................................................................ 3

Problems and Stakeholders ............................................................... 3

Accident Information of San Salvador city ........................................ 5

Specific Problem Areas ...................................................................... 6

Project Objectives .............................................................................. 8

Project Goal ........................................................................................ 8

Proposed Evaluation Method .............................................................. 8

The Swedish traffic conflict technique .............................................. 9

Project Implementation .................................................................... 11

Intersection 1: Av. España and 1 Calle Oriente ............................... 12

Location 2: Plaza El Salvador del Mundo west access ................... 15

Conclusions ....................................................................................... 17

References ........................................................................................ 19

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Introduction Every day, concern increases regarding traffic conditions in El Salvador’s capital,

San Salvador. Over 350,000 private vehicles use the city’s streets together with over 5000

public transportation vehicles. Congestion as well as pollution levels, as a result of

increasing demand for travel, become a growing concern for government officials. Many

problems related to this issue have their origin in the lack of an adequate control,

supervision and operation of key elements such as bus stops and intersections.

Proliferations of informal vendors that place vending stands on sidewalks and downtown

streets aggravate the problem. Actual public transportation routes operate without any kind

of coordination among them and government supervision is very poor. Among the main

problems the country is facing regarding its vehicle fleet is the elevated number of traffic

accidents. Although the country is one of the smallest in Latin America, El Salvador has

one of the top vehicular accident rates in the region.

This project aims at incorporating new methodologies for accident analysis to help

identify and prioritize traffic problem areas and to improve the ability of traffic authorities to

recommend measures to improve traffic conditions. Of particular interest will be the

application of the traffic conflict technique in locations were accidents are common to try to

promote measures to reduce the number of accidents, and increase government efficiency

for dealing with this issue.

Problems and Stakeholders San Salvador’s metropolitan Area (AMSS) has about 540 square km and suffers

from all the problems of a dense, capital city in the developing world. Congestion, traffic

accidents, pollution, lack of accessibility, poor public transport conditions, lack of a

pedestrian friendly environment, limited roadway space, illegal parking, street blocking,

illegal public transportation, insufficient police supervision, among others, all contribute to

an inadequate urban environment. It is also noticeable the lack of coordination between

different agencies involved in the regulation of the city´s infrastructure related services.

Transportation decisions are taken at the government level by the Viceministry of

Transport, whereas urban planning is undertaken at the local level by the Metropolitan

area planning office of San Salvador. There is practically no communication between

these two stakeholders. To make matters worse, road construction and land use are also

affected by the decisions of two other bodies, the viceministry of public works and the

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viceministry of housing and urban development. These two government bodies are,

together with the viceminstry of transport, part of the ministry of public works,

transportation, housing and urban development. Even when the three agencies are part of

the same ministry, effective communication among them is most of the time difficult to

achieve. Other factors such as street criminality and lack of funding need to be considered

when proposing different approaches to solving these issues.

Even though transportation laws and regulations are defined at the government

level, the viceministry of transport does not have its own operative body to make sure

regulations are abided by. This is the job of the national civil police, through its traffic

division, that comprises about 1800 traffic police officers for all the country. Despite this

number, given the shifts and police attention to other matters, it is estimated that there are

only about 900 effective traffic police officers to control the transportation system in El

Salvador.

The high number of traffic accidents affects of course road users the most, but other

stakeholders, such as emergency organizations and hospitals, and private entities like

insurance companies, are also affected by this problem.

Traffic chaos in San Salvador is worsened by the city´s inefficient transit system.

The following are some facts of the capital´s public transportation system:

• 195 Transit routes (97 AB, 98 MB) ,5467 vehicles (2764 buses, 2703 microbuses )

• Daily vehicle boardings over 1.8 million (buses 1.2 million - 68% & microbuses 0.6

million – 32%). Over 1.4 million person trips.

• Daily average pax/km for buses 4.46, with variation among routes between 2 & 10

pax.

• Daily average pax/km for minibuses 2.64, with variation among routes between 1 &

6 pax.

• Average age of buses over legal 15 year limit. (19 years), average age of minibus

fleet around 6 years.

• Routes with geographic affinity operate without any kind of coordination.

• The fleet runs daily about 75,000 km considered unnecessary according to

demand estimations.

The uncontrolled competition among operators contributes enormously to this chaotic

traffic system, generating unnecessary operating costs and increasing the number of

traffic accidents. The current public transport system does not allow for proper

planning or regulation according to actual demand nor the implementation of a

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coordinated operation system that is vital for the future sustainability of the city´s transit

service.

The following is information about the traffic accident situation:

Accident Information of San Salvador city1 40% of all the country’s collisions happen in San Salvador. The whole state of San

Salvador has about 886 km2 where nearly half of the country’s vehicle fleet circulate every

day. The following table shows the number of traffic accidents in the metropolitan region of

San Salvador, from the period of january to july of the years 2005 and 2006. There has

been an increase of 4% in the number of accidents registered, while the number of

vehicles has increased in a similar rate in the same period.

TRAFFIC ACCIDENTS

TOTAL ACC

TOTAL ACC %

Metropolitan Region 2005 2006

SUBTOTAL 7483 7827 4,6

One important factor affecting the high number of traffic accidents has to do with the

accelerated increase in motorization rates in El Salvador, the following table presents the

evolution of the size of the vehicular fleet in the country over the last ten years:

1 Source: Viceministry of Transport statistics.

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Specific Problem Areas Of all dangerous traffic accident sites in San Salvador, the intersection with most

accidents is Boulevard del Ejército and 50 Av. Norte. Main arteries Alameda Juan Pablo II

and Venezuela Boulevard also have some of the capital’s most dangerous intersections.

The first has six junctions among the most dangerous intersections in the capital and the

other boulevard has four.

Paseo General Escalón, another main artery of the city, has two intersections

among the 202 most dangerous in the capital, they are located only two blocks apart.

At the El Salvador del Mundo roundabout, 21 collisions were registered in the first

six months of the year 2006, about 6.25% of the total registered at the most dangerous

intersections of the capital (336 in total).

It is interesting to notice that 70.83% of the accidents in these intersections involved

private vehicles, versus 9.82% involving buses.

Of the 336 registered accidents in the main problematic intersections, 301, almost

90%, were collisions. There were 9 crashes and 18 runover pedestrians.

Not keeping a proper distance and invading lanes were the main causes of the

registered accidents (54.76% of the cases)

Ignoring or disobeying traffic signals was the cause of accidents in 21.72% of the

cases and driver distraction is listed as the accident cause 14.885% of the time.

There could be many causes behind the high number of accidents in these places.

At present time, current methods of gathering accident related information need to be

improved and some accidents are not even recorded and therefore the real numbers might

be even worse than the ones reported above. The following figures, taken from a local

newspaper3, illustrate the location of critical points in the city, and also present monthly

traffic accidents trends:

2 El Diario de Hoy, july 28, 2006 3 El Diario de Hoy, july 28, 2006

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Project Objectives The proposed Project aims at increasing the technical abilities of personnel at the

Viceministry of Transport to gather and analyze traffic accident related data and contribute

to reduce the number of accidents in the metropolitan region of San Salvador. To achieve

that goal, some of the intersections mentioned above will be selected and analyzed to

improve traffic conditions and apply measures to reduce accident risk. Of particular

interest will be the application of the conflict technique methodology to study the behavior

of traffic at these intersections. Traffic personnel at the Viceministry of Transport will be

trained to conduct the conflict surveys and it is expected that the conflict technique

methodology will be incorporated as a routine process in the traffic division of the

institution for the analysis of traffic problems. Improving the Viceministry’s ability to analyze

and respond to traffic accident problems will be the main objective of the proposed project.

Project Goal The goal of this project was to reduce traffic accidents in selected intersections at

least by 10% after the proposed measures were implemented. Personnel at the vice

ministry of transport were exposed and trained in new tools and methodologies to help

them contribute to improve traffic safety in the country.

The number of intersections was limited and the initiative was treated as a pilot

project that could be incorporated in the traffic engineering division annual program of

action for upcoming planning periods.

The goal was to have staff trained, intersections analyzed and measures

incorporated by December 2006, so as to have the first trimester of 2007 for evaluation

and comparison of accident behavior in the selected intersections.

Proposed Evaluation Method The selected way of evaluation was the comparison of accident data mentioned

above. It was also expected to conduct a before and after conflict study using the Swedish

traffic conflict technique at those intersections were measures were implemented.

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The Swedish traffic conflict technique

The origins of the traffic conflict technique (TCT) can be traced to the US to General

Motors, where a method was developed in the 1960´s to help understand and improve

auto technology performance regarding automobile safety. These original ideas were

further studied and analyzed in the 1970´s at the Department of Technology and Society at

Lund University in Sweden by a research group led by professor Christer Hyden.

Over a 20 year period, professor Hyden and his team refined his method and were

able to provide a simple yet powerful way to analyze and evaluate safety at a particular

location bypassing the need to collect large amounts of accident data. Another advantage

of the proposed methodology is that it does not require complex equipment making it

suitable for third world countries where resources are usually scarce.

The methodology has been popular in traffic research since the end of the 1970´s.

The Swedish conflict technique records and analyzes “conflicts”, which can be loosely

defined as interactions among two or more road users that according to their severity, may

or may not end up in a traffic accident. Severity for these events is based on the speed

and the time to accident, that is the time left until an accident would occur if the users don’t

perform an evasive action. Speed and time to accident had been used to define a curve

that helps to separate serious from non serious conflicts.

Serious conflicts are of particular interest for the technique since they can be used

as a “proxy” for traffic accidents. Since conflicts are more frequent than actual accidents,

their recording and analysis can contribute considerably in traffic safety research efforts at

different locations. The TCT allows assessing the risk of a location in terms of traffic

safety. Studies suggest that a few days of conflict observations provide better estimates of

a location accident potential than years of accident data. One of the reasons for this

situation is the fact that accidents can be events with low occurrence frequencies and

therefore can be subject to misinterpretation. Conflicts on the other hand are more

frequent and therefore better from a statistical perspective to provide information regarding

traffic safety.

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The following pyramid created by the technique developers shows the hierarchy of

interactions among road users; accidents are the tip of the pyramid and therefore the least

frequent events. Serious conflicts are more frequent and therefore their analysis can

contribute to the assessment of the safety level at a particular location of interest.

On the field, observers measure the speed of the road users when an evasive

action is taken as well as the distance from the point where a user begins the evasive

maneuver, (which may usually consist of breaking, swerving, accelerating or a

combination of these), to the potential collision point the interaction would have generated

had an evasive action not been taken by one or more of the parties involved.

Observers need to be trained to detect and record conflicts, as well as to assess

and register speed and distance. The following diagram presents the threshold between

serious and non serious conflicts defined by the technique developers:

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Accident data analysis has been the main source of information in El Salvador to

lead national efforts in traffic safety. Given the limitations of data collection procedures and

other situations typical of a third world country, the available accident data cannot be fully

trusted and can benefit from additional mechanisms that can help to better understand the

risks and dangers of El Salvador´s traffic. Accident data itself is limited, as many accidents

go unregistered by authorities. The Swedish conflict technique can therefore provide

helpful insight on traffic issues that can help make the national traffic system safer.

Project Implementation To conduct the project, a project proposal was prepared and handed to the

Viceministry of Transport authorities for approval. The initial proposal was to train the

entire traffic engineering unit personnel and conduct on site evaluations at different

locations with an elevated number of accidents. It was not possible to obtain approval for

this proposal, therefore only three people at the Viceministry, including the author, were

trained and conducted the field work.

Training was undertaken utilizing the available information from Lund University.

The direct support from Professor Christer Hyden was instrumental to clear doubts and to

improve field data recovery procedures.

After some field visits and the evaluation of the collected information, it was decided

that video collection of information would be used to allow for subsequent analysis at the

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office. By registering traffic operations with a video camera, it was possible to better

estimate speeds and to replay different incidents to improve analysis.

The team took advantage of the fact that some of the selected locations had traffic

control cameras installed nearby. It was possible to obtain access to the cameras and

install video recording devices at the national traffic operations center to obtain the footage

of the intersections and proceed to the analysis phase. At the beginning of the video

capture phase of the project, team members were directly shooting video at ground level.

It was possible to use an online video site to post some of the early footage of the field

visits and to share it with professor Hyden who kindly took a look at it and suggested to

take the videos from an elevated perspective to improve data analysis.

Two intersections were filmed, using cameras located near them that belonged to

the Vice ministry of transport.

The analyzed intersections had a high number of traffic accidents. Analyzing the

conflicts at each location was very insightful to better understand reasons behind the high

accident rates.

Intersection 1: Av. España and 1 Calle Oriente

This intersection ranked third among the most dangerous intersections in the

country, with 23 major accidents registered during the first half of 2006.

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In the picture above, the arrows indicate the direction of traffic at the intersection.

Both, Avenida España and 1 Calle oriente are one way streets in this area. Average daily

traffic at this intersection in the north south direction is 5848 light vehicles, 2469 passenger

vehicles and 2621 trucks/load vehicles. It is interesting to notice that for every 2 cars in the

intersection, there is one bus circulating. In the east west direction the average daily traffic

amounts to 7982 vehicles, out of which 3150 are cars, 3466 are passenger vehicles and

1366 are trucks/load vehicles. Buses outnumber light cars in the east west direction at this

location. After applying the traffic technique and analyzing the traffic operation at the

intersection, it was easy to identify a pattern and to define probable reasons for the high

accident rate.

Illegal bus stops were operating very near to two of the four access points to the

intersection (see the orange rectangles in the picture above, indicating the location of the

illegal bus stops), this situation contributed enormously to having an effective reduction of

the intersection capacity. Another problem that was detected was a lack of lane continuity

on the east west direction, where the street configuration changed from a three lane road

to a two lane road right after the intersection. This fact , together with the illegal bus stops,

actually generated a strong bottleneck at the intersection, that called for a high number of

vehicles on the east west direction maneuvering to change lanes and to use the only

available lane to continue their east west journey.

Red light running as well as intersection blockage were two other problems

identified at this intersection that contributed to the number of serious conflicts registered

in the area.

Video footage for this intersection was shot for two days, from 7:00 am to 6:00 pm,

during two weekdays. Previous visits to the site were undertaken in order to train staff in

identifying and recording serious conflicts.

The main conflicts identified at this location were generated by weaving maneuvers

due to lane reduction or lane blockage, as well as conflicts due to intersection blockage.

It was determined that the best way to improve traffic conditions at the intersection

was to have permanent police presence at the intersection to prevent buses from making

the illegal stops, as well as to prevent drivers from blocking the intersection. The following

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diagram displays the conflicts recorded at the intersection during the peak morning period

of 7:30 am to 8:30 am on day 2. The diagram is representative of other peak and non peak

periods.

The speeds at this particular location were not too high, with average speeds on the

east west direction of about 18km/h and average speeds on the north south direction of 35

km/h. The conflicts of vehicles going in the same direction and trying to avoid obstacles

such as lane blockage and lane discontinuity were far more common (on a 3 to 1 ratio)

than conflicts between vehicles in transversal directions. However, observations

suggested that these conflicts, given the higher speeds of the vehicles involved, could

probably lead to more serious accidents at this location.

In addition to suggesting more police presence for this area, it was also suggested

to change some of the routes that run through the area to reduce the number of buses, as

well as to relocate some of the bus stops nearby to promote an improved traffic flow that

could lead to less traffic accidents at the intersection.

The problem of lane continuity would require a geometric study that was also

recommended. Another possible measure that could be implemented in the future to deal

with problems at this location had to do with the installation of surveillance cameras that

could deter drivers from ignoring traffic signals.

It is interesting to notice that as a part of a larger plan to improve traffic flow in the

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city, police personnel was assigned to this intersection during the morning and afternoon

peak hours of traffic. A brief conflict study undertaken for three hours during the morning

peak period while police people were present in the area registered 40% less serious

conflicts proving the effectiveness of the measure.

Location 2: Plaza El Salvador del Mundo west access The west access intersection at El Salvador del Mundo Plaza was another site

selected for analysis given its high accident number. This area (all access to the

roundabout) registered 21 accidents for the first half of 2006. This location in particular is

not a regular intersection, but an access to a semi roundabout (see the picture below). It

had, however, a high amount of conflicts that were registered by the team after watching

video footage from an available traffic camera in the area. The green and red arrows in the

picture below indicate the movements that generate conflicts with the vehicles moving on

the east west direction. This area is particularly important for the east west traffic flow of

the city, with nearly 40,000 vehicles circulating through the area on a daily basis. Typical

peak hour traffic flows are also shown below:

The main conflict situation at this site was the problem a high number of cars were

having when trying to incorporate themselves to the east west direction of traffic, or trying

to continue on the south north direction, without finding an appropriate gap on the east

west traffic flow to allow for a conflict free incorporation. The high speed of the vehicles

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traveling west was the main reason identified for the conflicts occurring when a vehicle on

the roundabout coming from the south direction interfered with the traveling pattern of the

westbound vehicles. A large bus stop located nearby also promoted the problematic

situation since it contributed to visibility problems and lane obstruction on the east west

direction of flow in the area.

Conflicts were registered here for a period of two days from 7:00 am until 6:00 pm.

A plan already in progress to install a traffic light at this location was backed up by the

conflict study conducted for the project. It was possible to register conflicts after the traffic

light pilot installation period at the site. Horizontal Signaling was also improved at the site.

The installation and operation of the traffic light allowed the vehicles on the roundabout to

have a proper gap to continue in the north direction, as well as to incorporate to the east

west direction without interfering with the east west traffic flow, reducing conflicts

considerably. A conflict study of one day after the light was in operation demonstrated that

the conflicts between the westbound cars and vehicles going north or trying to incorporate

to this direction of traffic were eliminated using the traffic light.

Although there was enough evidence to suggest that the traffic light was an

effective measure against potential accidents at the intersection, the light was turned off

just after two weeks of operation, pending further analysis to make it a permanent

measure.

Besides the installation of the traffic light (an idea already in progress, but backed

by the conflict analysis), it was also suggested to eliminate south north movement at the

location. Given the conflict this maneuver generated, and the fact that less than 20% of the

vehicles on the roundabout were moving on this path, the team considered this to be a

feasible measure to improve traffic safety. This suggestion has not yet been implemented.

It was also possible to notice the negative effect the bus stop operating near the site

had on the traffic in the area. To improve traffic safety, relocating this bus stop or at least

generating an adequate bus bay so that traffic flow is not blocked and visibility affected

would be important measures for accident reduction.

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The following diagram shows the serious conflicts registered during a one and a half

hour period between 7:30 and 9:30 am at this location:

Conclusions

The application of the Swedish conflict technique in San Salvador proved to be a

very promising tool that can be easily incorporated in the Viceministry of Transport´s

efforts to tackle traffic safety problems. The methodology was easy to assimilate and

institution personnel were recording conflicts effectively just after a few training sessions.

Results improved significantly with the aid of video footage, that allowed the team to

review and replay different road users interactions.

The conflict technique has the potential to easily help conduct analysis of locations

were traffic accident registries are not available. Given the fact that statistical analysis and

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data gathering of accident information are not strong areas in El Salvador, the traffic

conflict technique can become a vital tool to overcome this situation.

The measures suggested to improve traffic safety at the points of study and that

were implemented were evaluated using the conflict technique. In both researched

locations, traffic conflicts were diminished after the proposed traffic measures were

implemented.

The sites selected to conduct the research and to apply the conflict technique were

based on historical accident data that ranked them as dangerous locations. The use of the

technique can also be used to develop a location ranking based on the number of conflicts

registered at spots and their severity that would overcome the need to have historical

accident data available.

It is expected that the results of this research can lead traffic authorities in El

Salvador to incorporate the Swedish conflict technique as a very useful tool in their efforts

to study and analyze traffic accidents problems all over the country.

Of particular interest for Salvadoran authorities should be the potential the

technique has to conduct before and after studies at locations where different measures

are applied to improve traffic safety, in order to evaluate in a short time period their

effectiveness.

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References

Hydén, C. (1987) - “The Development of a Method for Traffic Safety Evaluation:

the Swedish Traffic Conflicts Technique”, Department of Traffic Planning and

Engineering, Lund Institute of Technology, University of Lund, Sweden.

Pietrantonio, H. (1999) - “Avaliação Da Técnica Sueca De Análise De Conflitos

De Tráfego”, RELATÓRIO DE TRABALHO No.2/98, Brasil.

Anh, T. T. (2005) -“Conflict Technique Applied To Traffic Safety On The Model

Corridor Of Hanoi”, Proceedings of the Eastern Asia Society for Transportation Studies,

Vol. 5, pp. 1875 – 1890.

FHWA (1989) - “Traffic Conflict Techniques for Safety and Operations.

Observers Manual”, United States Federal Highway Administration, Publication No.

FHWA-IP-88-027.