Knowledge Resources

Based on previous deployments of adaptive signal control in London (England), the European Commission (EC) funded two new trials of SCOOT (Split Cycle Offset Optimization Technique) as part of the (1992-1999) European bus priority project known as INCOME (Integration of Traffic Control with Other Measures).

After extensive simulation testing SCOOT was deployed to quickly update signal timing and reduce corridor congestion on a 22 kilometer (km) section of Uxbridge Road between Uxbridge Town Center and Shepherd’s Bush in west London. The bus service in this area consisted of two overlapping express bus routes having a peak service of 20 buses per hour, and a demand of 60,000 passenger trips per day.

Prior to INCOME, Uxbridge road was severely congested and bus journey speeds were very low. Therefore, between 1993 and 1996 physical measures consisting of pre-signals, bus gates, and bus priority lanes were implemented. Annual surveys conducted between 1992 to 1995 indicated a 7 percent (4 minutes) decrease in bus journey time, and an increase in bus patronage.

Bus priority was enhanced during the project using SCOOT in conjunction with the following advanced traffic control and congestion management systems: Bus priority; Selective bus priority with automatic vehicle location (AVL); and Bus priority using gating strategies.

Bus Priority

During the trial period, in-vehicle systems were used to collect before-and-after bus performance data for each of the following.

• Extensions only strategy: Extended green time for buses detected towards the end of the normal green signal.
• Extensions and recalls strategy (normal priority): Extended green time as well as green signal recall for buses arriving on red (subject to safety constraints).
• Extensions and recalls strategy (high priority): Extensions and recalls strategy with additional benefits for buses even at the expense of added delay for general traffic.

The paper presented the following results for BUS SCOOT on Uxbridge Road.

BUS SCOOT STRATEGY	Average Reduction in Bus Delay	Average Reduction in Bus Delay Variability
Extension Only	5%	4%
Extension and Recalls (Normal Priority)	20%	8%
Extension and Recalls (High Priority)	19%	11%

No significant impacts were observed on other traffic.

Selective Bus Priority with Automatic Vehicle Location (AVL)

Automatic vehicle location (AVL) was installed to enhance fleet management through provision of real-time traveler information at bus stops. The AVL system evaluated on-time bus performance and determined individual bus priority requirements based on headway regularity algorithms.

Simulation results indicated minimum travel time and delay occurred when 40 to 100 percent of buses received priority.

Bus Priority Using Gating Strategies

The AVL bus priority strategy described above was most effective during periods of moderate congestion when spare green time was available to re-allocate buses. However, for saturated conditions, alternative strategies such as SCOOT "gating" were needed to protect buses from heavy congestion.

SCOOT "gating" was implemented near London in the region of Twickenham. The gating procedure was used to displace traffic queues on major bus routes and move congestion to adjacent roadways leading into town. The degree of saturation on major bus routes was monitored, and when unacceptable levels were reached, the green time on gated approach links was progressively reduced to limit traffic entering the critical link.

The field trials in Twickenham used automated before-and-after data collection techniques to compare Bus Priority with "gating" to Bus Priority alone. The following results were obtained for buses subject to AM peak congestion.

STRATEGY	Average Reduction in Bus Delay	Average Reduction in Bus Delay Variability
BUS SCOOT (Bus Priority Alone)	7%	10%
SCOOT (Bus Priority) & Gating	13%	12%

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