On Saturday, part of the northbound MoPac express lane opened to traffic, and more than 1,500 transactions were recorded in its opening weekend. The MoPac express lane project will add one toll lane in both directions between Parmer Lane and Cesar Chavez Street. Drivers pay a toll to use the lane, and the toll rate increases based on demand to keep the lane flowing at 45 mph. Rates go down as traffic goes down to encourage use. Here is what you need to know about the new express lane: 1. The only section open so far is a northbound express lane spanning north of RM 2222 to Parmer Lane. Traffic and revenue studies indicate this section of the project would have the lowest usage, but Mobility Authority officials expect this section to provide relief to drivers commuting north in the afternoon peak period, especially around Braker and Parmer lanes where traffic tends to bunch. Although full completion has been pushed back to early 2017, Mobility Authority Executive Director Mike Heiligenstein said the remaining lanes might not open until April. 2. More than 1,500 drivers used the toll lane on the first weekend. The lane opened at 8:45 a.m. Saturday, and on Saturday and Sunday, the Mobility Authority tracked 1,508 transactions in the section between 2222 and Parmer. As of 5:30 p.m. today, another 1,288 transactions occurred. Once the project is complete, travel times will be reduced to 10-12 minutes in the express lane versus 30-40 minutes in the main lanes, said Jeff Dailey, the agency’s deputy executive director. 3. The toll increased for the first time today at 4:40 p.m. to $0.39. The minimum toll rate is $0.25, and there is no maximum cost. Factors that determine the toll rate include the number of vehicles per hour, which the agency can track in each lane, as well as the speed of vehicles. The toll increases based on the amount of traffic in the express and main lanes. The Mobility Authority not only uses an algorithm to determine the toll rate but also with three employees, who operate the traffic management center from 6 a.m.-8 p.m. daily. Staffers watch the lanes through seven cameras throughout the open section, and the entire project has 17 cameras, said Greg Mack, assistant director of information technology and toll systems. “They look for traffic incidents or slowdowns and decide whether to raise the price,” he said. 4. What you see is what you pay. Drivers will only pay the rate they see displayed on the dynamic messaging sign at the entrance to the express lane even if the price changes while the vehicle is in the express lane. Drivers without a toll tag will pay a higher rate by mail.

The Mobility Authority will soon provide a way to look up the rate at the time of a transaction, Mack said.

5. Major traffic shifts are expected in November. In about two weeks, the agency expects to complete construction on the Steck Avenue bypass lane, which will allow drivers to avoid the intersection at MoPac and Steck. Around the same time, traffic on the southbound MoPac main lanes near Cesar Chavez Street could shift to its permanent location at the express lane overpass. Traffic on the northbound lanes will shift to the top of the northbound express lane underpass by late November, and the third main lane over Lady Bird Lake will reopen for the first time since early 2016.