Corridor Access Improvements

Drivers on I-35 use ramps to access the mainlanes. Some of the existing ramps do not meet current design standards and pose access challenges. Potential solutions under consideration include: ramp modifications, addition of auxiliary lanes (speed-change lanes) and collector-distributor (C-D) roads. Combined, these improvements will:

• Improve mobility along the corridor
• Improve safety along the corridor

Ramp Modifications

In some areas, like downtown Austin, the entrance and exit ramps do not meet current design standards because they are too short, too steep, too curved or too close together for optimal performance. Some exit ramps end too close to heavily congested intersections, forcing drivers to make sudden movements between frontage road lanes after exiting or causing ramp traffic to back up due to frontage road congestion. Mobility35 proposes to modify ramps in these areas in order to:

• Better manage traffic flow
• Maximize operational performance
• Increase safety

Auxiliary Lanes

The Mobility35 program proposes the addition of auxiliary lanes (or speed-change lanes) in several locations along the corridor. Auxiliary lanes function like an extension of the already available entrance and exit ramps, allowing a lane for drivers to accelerate and decelerate (merge) to match traveling speeds between mainlanes and frontage roads. These lanes are usually installed within the distance between an on-ramp and an off-ramp. Auxiliary lanes:

• Make merging safer
• Reduce disruption in traffic flow from merging traffic​

Collector-Distributor (C-D) Roads

Although many area drivers are unaware of having used them, C-D roads are already in place in several locations within the three-county area: southbound I-35 at Hester's Crossing, northbound Mopac at Parmer, and southbound Mopac at Duval. A C-D road is a one-way road next to and separate from the highway that allows entering and exiting traffic to merge without disrupting mainlane highway traffic. C-D roads allow traffic to bypass frontage road traffic signals at cross streets without being on freeway mainlanes. C-D roads are often used between closely spaced interchanges and are vital to the functionality of Diverging Diamond Intersections, another Mobility35 overarching concept. C-D roads:

• Provide a separate roadway for merging
• Keep through traffic separated from merging traffic to avoid disruptions in traffic flow
• Promote safer lane changing between mainlanes and frontage roads
• Allow traffic to bypass frontage road traffic signals at cross streets without being on freeway mainlanes