TfL expands SCOOT adaptive traffic management

Microsimulation traffic modelling has supported a further roll-out of SCOOT adaptive traffic signal control in London, demonstrating a 13% reduction in travel delays.

Cost saving:

• Modelling around 15% of cost of on-street trials.

Benefits:

• Average 12.84% saving in travel time delays.
• Average 04.6% saving in number of vehicle stops.

Development of a cost-effective traffic modelling system has led to a further major roll-out of SCOOT adaptive traffic management technology in London, says traffic and software programme director Gavin Jackman of UK transport consultancy 491 TRL.

The roll-out of SCOOT at 600 additional intersections, now at its midpoint, is a central plank in the Mayor of London’s policy objective of smoothing traffic flows to meet 1466 Transport for London’s (TfL) network management duty under the UK’s 2004 Traffic Management Act. At the same time, the use of more responsive and versatile traffic control is seen as making an important contribution to the reduction of emissions and pollutants – another policy priority. Previous experience in targeting these goals was already indicating the need for further deployment of SCOOT in London, where it has been replacing previous fixed-time installations since 1985.  

Low cost evaluation

But TfL first wanted cost-effective quantification of the benefits. “Such confirmation typically emerges from local evidence. But the high cost of on-street trials can be a deterrent to the necessary research,” Jackman told an IBEC (International Benefits, Evaluation & Costs) working group session held at the October 2012 6456 ITS World Congress in Vienna.

Experience suggested that modelling was likely to come out at around 15% of the on-street cost. To meet the challenge, TRL developed a model with an urban traffic control 3989 Vissim microsimulation interface, connecting SCOOT to multi-modal traffic flow simulation software developed by German company 3264 PTV Planung Transport Verkehr AG. This modelled three traffic management scenarios for comparison: fixed time; SCOOT; and SCOOT raised cycle time. It modelled four traffic flow scenarios: existing flow; flow increased by 10%; flow increased by 20%; and flow affected by incidents. Three outputs were produced: vehicle delays; stops; and emissions. The modelling was based on two busy central London intersections where existing microsimulation models and SCOOT were available – Victoria and Tavistock Place.

Results validated

Over a typical five-hour weekday morning peak period, the model predicted savings in both locations of 100l of fuel consumed and 236kg of CO2 emitted. Vehicle stops and delays both reduced with SCOOT being activated. The results are shown in Tables 01 and 02. The emissions results are as in Tables 03 and 04.

Table 01: Base flow SCOOT benefits

	Reduction in delays %	Reduction in stops %
Victoria	11-16	10-17
Tavistock Place (all scenarios)	08-29	06-25

Table 02: Incident flow SCOOT benefits

	Reduction in delays %	Reduction in stops %
Victoria	12	10
Tavistock Place	14	8

Table 03: Base flow emissions reductions

	Reduction in NOx%	Reduction in PM%	Reduction in Carbon%
Victoria	8	5	6
Tavistock Place	3	1	3

Table 04: Incident flow emissions reductions

	Reduction in NOx%	Reduction in PM%	Reduction in Carbon%
Victoria	9	6	7
Tavistock Place	7	3	8

The models predicted annual user benefits, per junction, of between £89,200 and £107,100, with an overall user benefit in the first year, per node, of £90,000 (2009 value of time) excluding vehicle operating costs and the social cost of carbon reductions.

The modelling results have been validated and show that overall, across the 600 junctions, SCOOT is delivering an average 12.84% reduction in delays and 4.6% reduction in the number of times that vehicles have to stop as they travel through the network.

SCOOT (Split Cycle Offset Optimisation Technique), developed by TRL and now jointly owned by TRL, Peek and 189 Siemens, is deployed in most major urban centres in the UK and over 250 cities worldwide. It was voted most transformative network management tool at 136 Traffex 2011 in a poll of transport community members.