In my last post we discussed the general importance of collecting work zone data before any temporary traffic control is installed. This was mentioned as an important lesson learned by several of the states that attended the peer-to-peer exchange May 21 and 22 in Iowa. They all wished they had accurate baseline measurements with which to compare.
In a later presentation W. D. Baldwin of HDR Engineering advocated the same thing but for different reasons. He said that by collecting baseline data before construction begins you will make better decisions about when to take a lane.
He suggested watching traffic counts. He uses PCE’s (passenger car equivalents). Most freeway lanes can handle about 1600 PCE’s per hour before queuing begins. If you measure counts over all lanes before you close one or more lanes, you will be able to see if the resulting counts will approach that number in the remaining open lane(s). If so, you should delay the work.
Many construction projects are bid with pre-planned work windows. These are traditionally based on historical data. But as we discussed in the last post, counts often differ significantly due to a variety of reasons. Mr. Baldwin explained that by measuring counts just before you start, you will make far better decisions about when to close lanes and when to open them back up.
This may be especially important for maintenance work and other short-duration work zones. Maintenance crews could place a sensor near the start of their proposed taper when they arrive at the work location. They could then hold their tailgate meeting with the crew to discuss that days’ work while the Traffic Management Center monitors counts. As soon as counts are low enough, the TMC could call the supervisor and tell him it’s OK to close the lane.
The other side of this same coin is some form of variable work windows. Utah DOT is considering a system of incentives or disincentives where the contractor decides when to work and when to stop. They are penalized when speeds drop below a certain level, or when queues exceed some agreed length, or some other measure is exceeded. Both the DOT and the contractor see the data in real time so everyone is on the same page. It gives the contractor the opportunity to get more done when traffic thins out.
In cities like Los Angeles and San Francisco work windows can be as little as 4 or 5 hours. Traffic control takes a good hour to set up and tear down leaving the contractor as little as 2 hours to work. In cases like these, if a variable system got him just one more hour twice a week, it would equal a 20% increase! That would result in faster completion and reduced exposure – increased safety and reduced costs – a “win-win” in anyone’s book!