91X does 40% traffic with 33%

Greg Hulsizer gen manager for the 91 Express (91X) lanes project in Orange County California told an Eno Foundation/FHWA symposium in Washington DC recently that his lanes are carrying 40% of the peak hour traffic in the corridor with 33% of the capacity. 91X has 2-lanes each direction in the median of 4-lanes each direction of the untolled freeway. Over the whole 24 hours 91X only gets 11% of the total traffic. He showed a graph for eastbound traffic which is the PM peak direction in which from 2:30PM onward the freeway lanes have reached a maximum throughput and all the spillover is going to the X-lanes. During the period of worst congestion on the freeway lanes when traffic flow has broken down seriously a situation arises where 91X traffic is northeast of freeway traffic on a graph of volume and speed. That graph is the famous ‘backward-bending curve’ or parabola.

The FHWA/Caltrans supported independent reviewer Ed Sullivan presented data in one of his reports two years ago showing similar throughput per lane per hour but with X-lanes at about twice the average speed of freeway traffic. That puts 91X due north on the parabola. But Hulsizer says the situation now is even more favorable for 91X motorists because the freeway capacity declines well below maximum throughput as speeds go lower with overloading.

91X tolls range between 75c and $4.25 according to a toll schedule by hour with the current toll posted on a variable message sign 1.2km (3/4mi) before the entry point. In order to maintain free flow, California Private Transp Co (CPTC) the operators of 91X look to upping a toll rate when they are consistently getting 1,700 veh/lane/hr.

91X has 130k customers with tags and is also used by some of the 400k tagholders at the county TCA toll roads agency. It does an average 25k tolls/day. Hulsizer says revenue is currently running at about $21m/yr with $9m operating costs.