Knowledge Resources

In October 2004, the California Department of Transportation (Caltrans) conducted a 'Rapid Rehab' project on a heavily traveled section of Interstate I-15 in Devore, California. In order to rebuild a 2.8 mile stretch of roadway in 18 days (9 days for each direction), round-the-clock (24/7) counter-flow lane operations were performed and Automated Work Zone Information System (AWIS) technologies were deployed to limit traffic disruption.

A pre-construction traffic analysis was conducted using the Highway Capacity Manual (HCM 2000) with hourly traffic data (March 2002) to determine the maximum peak hour delay to expect in the work zone during construction. The analysis assumed that “without” AWIS there would be a 10 percent reduction in traffic demand as a result of natural traffic diversion. The analysis showed that with a 10 percent reduction in traffic demand, the maximum delay within the work-zone would be approximately 95 minutes for weekday PM peak period traffic headed northbound. Caltrans, however, indicated that a 20 percent reduction in peak period traffic demand was necessary to ensure success of the extended closure project and 24/7 operations. Thus, it was estiamted that if AWIS could contribute to a 20 percent reduction traffic demand, the maximum work zone traffic delay would be only 50 minutes. Caltrans indicated that this level of potential delay was acceptable considering the reconstruction project would have taken about 10 months to complete using a traditional approach of nighttime closures.

The northbound roadbed was closed first, switching traffic to the southbound side through median crossovers installed at each end of the construction work zone. A Quickchange Moveable Barrier (QMB) system was used to switch the two-by-three lane configuration twice each day in an operation that took less than 30 minutes in live traffic.

The AWIS enabled travelers to observe traffic conditions before they entered the work zone and choose alternate routes based on guidance from roadside dynamic message signs (DMS). A central computer system was used to collect speed data from roadside detectors, estimate current travel times, and disseminate the real-time information on DMS and the project website. The project website was part of an extensive public outreach campaign designed to promote the system, and help travelers identify available detour routes and plan trips accordingly.

The AWIS provided updated travel time information every 10-minutes enabling travelers to make timely travel decisions. The DMS system displayed one of six different messages depending on the level of congestion detected in the work zone (Level-1 free flow, to Level-3 severe congestion). When travel time estimates exceeded 50 minutes through the work zone, and severe congestion was detected, the central computer system automatically crosschecked traffic conditions on alternate routes (i.e., I-10 eastbound) to see if a detour recommendation was warranted. If the alternate route was experiencing free flow conditions, the detour recommendation was flashed on and off in sequence with the work zone travel time information (e.g., “TRAVEL TIME 50 MIN FROM I-15/I-210 TO SR-138” and “DETOUR TO I-10 EAST”).

Traffic was monitored before and during construction to capture traffic pattern changes as they related to work zone construction activities. Microwave sensors were used to monitor traffic in the work zone, and the California Freeway Performance Measurement System (PeMS) was used to monitor traffic outside of the work zone and on neighboring freeways (I-10 and I-215). Traffic flows on major freeways were measured for 14 days before construction and 18 days during construction. Traffic data on arterials were collected for four days before and four days during construction.

RESULTS

During the construction, the AWIS successfully performed its automated travel time estimation function, producing estimates within a 10 percent error range compared to actual travel times measured by probe vehicles. The AWIS deployment greatly reduced traffic demand through the work zone by diverting drivers to major freeway detour routes.

• Average Daily Traffic (ADT) volume on I-15 southbound decreased by 19 percent while ADT volume on I-215 southbound (I-15 southbound detour route) increased by 15 percent.
• ADT volume on I-15 northbound decreased by 16 percent while ADT volume on I-10 eastbound (I-15 northbound detour route) increased by 10 percent.
• ADT volumes on the adjacent major arterials increased by only 2 percent.

Field data indicated that the maximum average peak delay with AWIS was 45 minutes, approximately 50 percent less than the expected maximum delay without AWIS.

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