Swakeleys Roundabout –Traffic Modelling Update

26 September 2018

• VISSIM modelling update

• TfL response to Hillingdon’s request for further information

• Next steps

• AOB

Agenda

Following further Audit in line with TfL’s MAP process the VISSIM has been amended and re-run, with a small change in results for the “+HS2” scenario only.

As the HGV figures have been updated in both Future Base and Future Proposed, the overall impact on the results is very small. The SATURN model is not affected.

We are confident the figures reflected are robust.

VISSIM Model Update

The next few pages will show: • The predicted local impacts of the scheme

to improve Swakeleys Roundabout.

• The key journey times – for both general traffic and buses – in the Future Base and Proposed, with and without HS2 traffic

• The impact in the AM (0730-0830) and PM (1700-1800) peak

VISSIM Model Update

Local Modelling AreaA B

C

D

E

F

G

H

Local Bus Routes

U1

U9

U10

VISSIM Modelling: Traffic Journey Times Comparison

Base 2021 vs Pro 2021 (no HS2 traffic)Base Model Journey Times

(Minutes)Proposed Model Journey Times

(Minutes)Difference between Base and

Proposed (Minutes)

From To AM PM AM PM AM PM

A to E Harvil Road A40 Eastbound 9 to 10 5 to 6 11 to 12 5 to 6 1 to 2 0 to 1

A to G Harvil Road Harefield Road 9 to 10 5 to 6 11 to 12 5 to 6 1 to 2 0 to 1

B to F Breakspear Road Park Road 14 to 15 3 to 4 10 to 11 3 to 4 - (4 to 5) neutral

C to E Swakeleys Road A40 Eastbound 10 to 11 3 to 4 6 to 7 3 to 4 - (4 to 5) neutral

D to H Warren Road A40 Westbound 2 to 3 2 to 3 2 to 3 2 to 3 neutral neutral

E to A A40 Westbound Harvil Road 4 to 5 7 to 8 4 to 5 7 to 8 neutral neutral

E to F A40 Westbound Park Road 2 to 3 4 to 5 2 to 3 2 to 3 neutral - (2 to 3)

F to B Park Road Breakspear Road 4 to 5 19 to 20 5 to 6 7 to 8 0 to 1 - (10 to 15)

F to E Park Road A40 Eastbound 2 to 3 17 to 18 2 to 3 4 to 5 neutral - (10 to 15)

F to H Park Road A40 Westbound 1 to 2 16 to 17 1 to 2 3 to 4 neutral - (10 to 15)

G to A Harefield Road Harvil Road 4 to 5 9 to 10 4 to 5 6 to 7 neutral - (3 to 4)

H to C A40 Eastbound Swakeleys Road 8 to 9 10 to 11 7 to 8 11 to 12 - (1 to 2) 0 to 1

H to D A40 Eastbound Warren Road 7 to 8 10 to 11 6 to 7 9 to 10 - (1 to 2) - (0 to 1)

H to F A40 Eastbound Park Road 7 to 8 9 to 10 5 to 6 9 to 10 - (1 to 2) neutral

VISSIM Modelling: Bus Journey Times Comparison

Base 2021 vs Pro 2021 (no HS2 traffic)Base Model Journey Times

(Minutes)Proposed Model Journey Times

(Minutes)Difference between Base and

Proposed (Minutes)

From To AM PM AM PM AM PM

U1 NB Park Road Swakeleys Road 7 to 8 15 to 16 7 to 8 9 to 10 neutral -(6 to 7)

U1 SB Swakeleys Road Park Road 11 to 12 7 to 8 9 to 10 7 to 8 -(2 to 3) neutral

U9 NB Harefield Road Harvil Road 4 to 5 8 to 9 4 to 5 5 to 6 neutral -(3 to 4)

U9 SB Harvil Road Harefield Road 4 to 5 2 to 3 3 to 4 2 to 3 neutral neutral

U10 NB Harefield Road Woodstock Drive 3 to 4 6 to 7 4 to 5 4 to 5 0 to 1 -(1 to 2)

U10 SB Woodstock Drive Harefield Road 2 to 3 2 to 3 2 to 3 2 to 3 neutral neutral

Note on Bus Frequencies

Bus modelling results are based on a very low data sample and are only listed as anecdotal evidence.

To assess scheme performance it is best to consider general traffic journey time comparisons.

Bus Route

Buses / Hr each way

U1 5

U9 3NB, 2SB

U10 1

Modelling Results Summary - Legacy Scheme

VISSIM Modelling: Traffic Journey Times Comparison

Base 2021 + HS2 vs Pro 2021 + HS2Base Model Journey Times

(Minutes)Proposed Model Journey Times

(Minutes)Difference between Base and

Proposed (Minutes)

From To AM PM AM PM AM PM

A to E Harvil Road A40 Eastbound 9 to 10 5 to 6 11 to 12 6 to 7 1 to 2 0 to 1

A to G Harvil Road Harefield Road 9 to 10 5 to 6 11to 12 5 to 6 1 to 2 0 to 1

B to F Breakspear Park Road 14 to 15 3 to 4 10 to 11 3 to 4 - (3 to 4) neutral

C to E Swakeleys Road A40 Eastbound 10 to 11 3 to 4 6 to 7 3 to 4 - (4 to 5) neutral

D to H Warren Road A40 Westbound 2 to 3 1 to 2 2 to 3 2 to 3 neutral neutral

E to A A40 Westbound Harvil Road 4 to 5 5 to 6 5 to 6 4 to 5 0 to 1 - (0 to 1)

E to F A40 Westbound Park Road 2 to 3 3 to 4 2 to 3 2 to 3 neutral - (0 to 1)

F to B Park Road Breakspear Road 4 to 5 8 to 9 5 to 6 5 to 6 0 to1 - (3 to 4)

F to E Park Road A40 Eastbound 2 to 3 6 to 7 2 to 3 2 to 3 0 to 1 - (4 to 5)

F to H Park Road A40 Westbound 1 to 2 6 to 7 1 to 2 2 to 3 neutral - (4 to 5)

G to A Harefield Road Harvil Road 4 to 5 5 to 6 4 to 5 4 to 5 - (1 to 2) - (0 to 1)

H to C A40 Eastbound Swakeleys Road 9 to 10 11 to 12 7 to 8 8 to 9 - (2 to 3) - (3 to 4)

H to D A40 Eastbound Warren Road Low sample 11 to 12 6 to 7 7 to 8 ~ - (3 to 4)

H to F A40 Eastbound Park Road 7 to 8 10 to 11 6 to 7 7 to 8 - (1 to 2) - (3 to 4)

VISSIM Modelling: Bus Journey Times Comparison

Base 2021 + HS2 vs Pro 2021 + HS2Base Model Journey Times

(Minutes)Proposed Model Journey Times

(Minutes)Difference between Base and

Proposed (Minutes)

From To AM PM AM PM AM PM

U1 NB Park Road Swakeleys Road 7 to 8 10 to 11 7 to 8 7 to 8 0 to 1 -(3 to 4)

U1 SB Swakeleys Road Park Road 11 to 12 7 to 8 8 to 9 7 to 8 -(2 to 3) neutral

U9 NB Harefield Road Harvil Road 4 to 5 4 to 5 4 to 5 3 to 4 0 to 1 -(1 to 2)

U9 SB Harvil Road Harefield Road 4 to 5 2 to 3 3 to 4 2 to 3 -(0 to 1) neutral

U10 NB Harefield Road Woodstock Drive 3 to 4 4 to 5 4 to 5 3 to 4 0 to 1 -(1 to 2)

U10 SB Woodstock Drive Harefield Road 2 to 3 2 to 3 2 to 3 2 to 3 neutral neutral

Note on Bus Frequencies

Bus modelling results are based on a very low data sample and are only listed as anecdotal evidence.

To assess scheme performance it is best to consider general traffic journey time comparisons.

Bus Route

Buses / Hr each way

U1 5

U9 3NB, 2SB

U10 1

Modelling Results Summary – HS2 Traffic

Modelling Results Summary

• Capacity improvements on the roundabout and on the north side, combined with the gaps in traffic brought by signal control, means that the roundabout can cope with more traffic and reduce the peak hour queuing problems.

• The northbound exit from the roundabout has been improved by re-designing for more capacity at the merge and right turn into Warren Road and by linking the pedestrian crossing with the new signals to progress the main flow of traffic. In general this has reduced congestion on the west side of the roundabout.

• Buses benefit from the increase in capacity, with a potential negative impact on the southbound U9, which may be delayed on Harvil Road due to the increased give-way conflict at the roundabout from higher northbound flow.

• Greater throughput of traffic at Swakeleys Roundabout reduces queueing into this junction, but it should be recognised that this traffic would likely increase congestion further downstream at Ickenham Pump and St. Andrews Roundabout. The final strategy will be able to balance this to some degree when implemented.

Modelling Technical Assurance • A base VISSIM model was produced that replicates current traffic conditions. The

model was built using survey data from October 2017, calibrated and validated against this data as well as engineering experience and site observations.

• Traffic distribution in all future models is based on SATURN reassignment. The SATURN model reassigns traffic according to cost, with faster routes (governed by distance and traffic delay) being cheaper. The model used is WeLHAM 2021.

• Traffic movement increases and decreases are taken from the SATURN and programmed into the VISSIM. The future VISSIM models all contain different traffic levels as a result of this process.

• VISSIM is a tool used to assist design and assess the network impact of proposals. It is a detailed and powerful modelling tool that can help traffic engineers and transport professionals to predict the relative impact of a proposal.

• In developing future scenario modelling an additional element of prediction is introduced from the reassignment process. Overall, traffic levels in the 2021 future proposed VISSIM scenarios are higher than the 2017 surveyed flows.

• Journey time comparison outputs are banded to show that there is a margin of error in the results.

TfL response to LBH request for further information

• Modelling HS2-HGV data

• HS2 workforce travel

• Refresh of report and maps

• Southbound peak time CCTV prohibition – The Drive

• Signal timing

• Raw traffic count data

Items for clarification

Next steps

• TfL/HS2 to commence public engagement -9 Oct

• Final drafting of agreements to be in place

• LB Hillingdon to make decision on scheme –critical