Greek inventor Archimedes once said, “The shortest distance between two points is a straight line.” This idea is such a simple concept and can be seen in so many parts of life. For example, babies understand this concept when crawling towards their parents, and predators understand this notion when chasing their prey.
In engineering, we see this theory when drivers try to get to the fast-food restaurant just across the street. Drivers often say, “Why can’t I make this left turn! McDonald’s is right there. You’re telling me I have to make a U-turn?” Access management is why.
The Federal Highway Administration defines access management as the proactive management of vehicular access points to land parcels adjacent to all manner of roadways. I consider it a balancing act – we want to provide mobility for through traffic while also providing accessibility to adjacent properties. The figure below illustrates the relationship between mobility, accessibility, and roadway types.
Source: Alabama Department of Transportation
Successful implementation of access management can increase roadway capacity, shorten travel time for motorists, and reduce crashes. The FHWA has found a 25-31% reduction in crashes along urban/suburban arterial roadways after a corridor access management plan has been implemented.
One of the main reasons for crash reductions is the lowering of access points. More access points equal more conflict points, leading to more slow-downs and more crashes. To help control the number of conflict points or the number of accesses along a roadway, traffic engineers employ a variety of techniques, including:
- Installing raised medians
- Consolidating two closely spaced driveways into one
- Restricting turning movements at an intersection
- Constructing service/frontage roads
- Optimizing traffic signal spacing
- Limiting the number of median openings
- Constructing turn lanes
To codify these practices, most states across the country have developed their own access management guidelines. The Alabama Department of Transportation (ALDOT) published their first Access Management Manual in 2014. It has since been used by ALDOT staff to provide a basis for approving or denying access permits. Along the way, ALDOT received input from their staff and consultants about desired changes to the manual. So, in 2020, Sain Associates was contracted along with Skipper Consulting to update the manual. We started our project by conducting interviews with ALDOT staff across the state to get their feedback on the current manual. ALDOT selected a steering committee with expertise in safety, design, pre-construction, maintenance, legal, and right-of-way to help guide the updates. We also reviewed other state DOT’s access management guidelines and the Transportation Research Board’s Access Management Manual and Access Management Application Guidelines.
The manual includes the following topics, among others:
- Principles of access management
- Access management strategies
- Traffic impact study requirements
- Access design
- Turn lane design
- Retrofit techniques
Some of the sections in the manual from 2014 will go unchanged, but we are updating large portions of it to align with the state of the practice and clarify any sections that were found to be ambiguous. We are nearly finished with the updates, and we’ll soon be scheduling one-day training sessions to present the changes to ALDOT staff. We intend for this updated manual to help guide transportation professionals to protect the traveling public’s safety, health, and welfare.
While the shortest route between two points is a straight line, it might not be the safest. That’s why we need access management.