Knowledge Resources

This project evaluated the impacts of a transit signal priority system in Southampton, England. In-pavement loop detectors were installed on five links approaching three SCOOT (Split Cycle Offset Optimization Techniques) controlled junctions. When the magnetic inductance signature of a bus was detected, the loops triggered priority control software at the signal controller and granted the bus priority. A new green phase or green phase extension was granted depending on a pre-defined set of signal control parameters that gave buses a high level of priority over other traffic.

The following sections of roadway were equipped:

• Old Northam Road approaching Six Dials.
• New Road approaching Six Dials.
• Commercial Road (westbound) approaching junction with Havelock Road.
• West Park Road (eastbound) approaching junction with Havelock Road.
• West End Road (westbound) slipway.

At each site, on-street surveyors were positioned at the bus detector and at the location of the traffic signal stop line to record the time at which buses passed by. Each link was surveyed for one week with and without the priority system in operation. Field data were collected during the AM peak (07:30-09:30), AM off-peak (10:00-1200), PM off-peak (13:30-15:30) and PM peak (16:00-18:00) periods for a total of 36 hours per week. Data were not collected during the Monday AM peak period and the Friday PM peak period since these peak periods were not typical of other weekdays.

Bus journey time data were used to evaluate system impacts on bus speeds, traffic delays, and system operations. Impacts on bus emission levels and fuel consumption were calculated using speed-related emissions factors derived from a national emissions database. Impacts on other traffic were assessed using general traffic data collected from loop detectors at each SCOOT intersection.

FINDINGS

The relatively high priority given to buses improved bus performance and reduced bus delay, bus fuel consumption, and bus emissions; however, because such a high level of priority was granted, additional delays were incurred by other vehicles which resulted in an overall increase in fuel consumption and emissions for all listed pollutants except Sulphur (S), Nitrogen oxides (NOx), and particulate matter (PM).

The Transport Research Laboratory (TRL) authors noted that the reductions in NOx and PM were important since these compounds were more likely to exceed acceptable levels in urban environments.

IMPACTS OF TRANSIT SIGNAL PRIORITY (TSP)	Buses	Other Traffic	Overall
CO emissions	-24%	9%	8%
CO2 emissions	-13%	6%	3%
HC emissions	-25%	7%	4%
S emissions	-13%	6%	0%
NOx emissions	-16%	-2%	-9%
PM emissions	-22%	3%	-12%
Fuel consumption	-13%	6%	3%

(Data excerpted from: TRL 413, Table 19 - Summary of Impacts)

Notes:
See Also:
Monitoring and evaluation of a public transport priority scheme in Eastleigh, TRL 411.