I-80 Smart Corridor sets the ITS standard for California's Bay Area
First publishedin ITS International
Long service life and short repair times were key benefits of the LED signs selected
Colin Sowman looks at California’s ‘smartest’ road which will open this spring to counter congestion and accidents on one of the Bay Area’s busiest interstates.
Interstate 80 (I-80) is one of the busiest roads in the San Francisco Bay area with up to 270,000 vehicles using the corridor every day. The section between the Carquinez Bridge in Crockett and the Bay Bridge not only suffers congestion during the working week but also at weekends. Traditional remedies such as building additional lanes (there are already up to six lanes in each direction) would cost several million per dollars per lane mile and was not an option as the interstate is bounded by an environmental area and housing developments.
So in order to ease the congestion in a shorter timeframe, and at a lower cost, the 31.4km (19.5 mile) section between the Carquinez and Bay bridges will become a Smart Corridor. Transit services will also be improved.
Modifications to the I-80 corridor started in late 2011 as a partnership between the California Department of Transportation (Caltrans), the Alameda County Transportation Commission (ACTC), and the Contra Costa Transportation Authority (CCTA). When the $79 million Smart Corridor opens in early 2015, it will be one of the most comprehensive intelligent transportation systems in California. It will employ a network of integrated electronic signs, ramp meters and other elements to improve travel time reliability and reduce accidents and associated congestion.
Lane use and advisory speed limit signs under test before installation
There are 44 on-ramps along this section of the I-80 with many providing access to San Pablo Avenue. This runs parallel to the interstate and is already benefitting from a degree of coordination of the 85 traffic signals along the corridor, including transit priority. However, traffic from San Pablo Avenue and other arterial roads entering the I-80 not only contributes to daily congestion, it also increases the potential for accidents in the corridor as vehicles from the on-ramps merge on the freeway.
Previously this section of the I-80 has not been equipped with variable message signs for traffic management, so when an incident occurs motorists are unaware of the impending sudden slowdown ahead. This can lead to drivers making abrupt lane changes, resulting in secondary accidents that worsen congestion and delay emergency vehicles, resulting in slower incident response and recovery times. The situation can become something of a vicious circle.
As the traffic backs up some motorists will exit onto San Pablo Avenue to avoid the jam, but the traffic signals on San Pablo Avenue and other arterial roads are not equipped to handle this sudden increase in traffic volume. All too often the result is gridlock that impacts motorists, bus operations, police and emergency vehicles on the arterial streets.
Compounding the situation on the arterial streets is that without knowing the location of the accident, instead of rejoining the interstate the diverting motorists remain on the city streets for longer than necessary, so the traffic jams persist. Motorists who decide not to detour are given no indication as to how long it will take them to reach their destination. It is an extreme example of the conundrum many traffic managers, and indeed motorists, will recognise.
Map of the I-80 Smart Corridor
Central to the Smart Corridor’s operation is adaptive ramp metering which will be used to regulate the volume of traffic entering the interstate at any given intersection. Loops in the on-ramps will detect the length of queues waiting to enter the I-80 and will communicate with the metering systems on adjacent ramps to alleviate backups on local streets while maintaining travel times for vehicles already on the interstate.
Throughout the wider corridor area, transit signal prioritisation will be installed at approximately 100 intersections - including at ramp meters where there are HOV lanes to enable transit vehicles to bypass the queues. Emergency vehicle detection sensors will be installed at approximately 50 intersections or ramps.
Around 50 existing or new closed-circuit television (CCTV) cameras will be used to monitor the Smart Corridor section of the I-80 and for incident management. In the event of an accident, a new incident management system will give motorists real-time information about blocked lanes ahead enabling them to move over in a controlled fashion and thereby creating easier access for emergency response vehicles.
The result is expected to be fewer unexpected lane-changes which will minimise the risk of secondary accidents resulting in smoother traffic flow, and faster response to emergencies. According to Ivy Morrison, public information officer for the project: “It’s about making the best use of existing infrastructure.”
Real-time traffic information, such as blocked lane warnings and advisory variable speed limits will be displayed on 133 new signs - including those mounted on 11 overhead gantries that have recently been installed along the westbound I-80. Each gantry will carry a combination of lane use signs, advisory speed signs and variable message signs while others signs and information boards will be pole mounted at other locations. The signs use the latest high intensity LEDs which are energy efficient and easily maintained (the mean time to repair is 10 minutes) with minimal scatter to cut light pollution and are set in black surrounds to make them easily readable.
Each ganrty carries several types of sign
While the I-80 Smart Corridor will pass through nine cities and two transit agencies (the Alameda-Contra Costa Transit District and Western Contra Costa Transit Authority) to work efficiently the monitoring, signalling and control systems must function as a single entity. For that reason all the components are connected in a single network with the ramp meters and real-time message signs integrated with, and managed from, the traffic management centre at Caltrans’ Bay Area headquarters in Oakland. This integration of real-time information into a region-wide system will also include the management and coordination of traffic along San Pablo Avenue in the event of an incident in the I-80.
During normal operations the local traffic signals will be controlled by the local agency and the transit agencies will monitor transit priority during both normal and incident management conditions.
Various controller upgrades or new controller communications (Ethernet modules and the like) are being installed at about 250 traffic signals on San Pablo Avenue and other local streets. About 30 existing or new microwave vehicle detection stations will be used to monitor traffic counts on local streets, and to enhance the system’s vehicle detection capability additional cameras or magnetometers are being installed at about 70 intersections.
Signage along San Pablo Avenue is being improved and extended as part of the Smart Corridor project
Work on San Pablo Avenue was finished last autumn and particular improvements include the installation of ‘Trailblazer’ signs which inform drivers detouring around an accident when they can return to the interstate. While much of San Pablo Avenue already has traffic signal interconnect for efficient signal timing coordination and progression there will be further improvements to the signals on it and the crossing arterials. This will include signal coordination, and transit signal priority will be used to improve traffic flow throughout the corridor during normal operating conditions, with additional signal interconnect on crossing arterials to improve the flow of traffic between San Pablo Avenue and I-80.
In addition, the transit service prioritisation that exists along much of San Pablo Avenue (which is also used for emergency vehicle preemption) will be extended to the WestCAT service area and crossing arterials.
In the event of an incident on the I-80 the timing of the upgraded signals along the arterials will be modified to increase the traffic throughput and reduce the recovery time to normal conditions.
Traffic information boards, which will go live a few months after the Smart Corridor opens, will be placed at six areas along I-80 at points where motorists can decide whether to remain on the I-80 or take another route. These large electronic signs have colour graphic capability to provide more information to drivers than the traditional changeable message signs. The Trailblazer signs along San Pablo Ave will then inform drivers who have diverted from the I-80 when they have passed the incident and can return to the interstate.
The result is expected to be a reduction in congestion and secondary accidents on I-80 and consequently fewer vehicles detouring onto San Pablo Avenue. This will have been achieved without requiring additional land or compromising the capacity of the free-use lanes.