Roadway Access Spacing

By Matt Riddell

With many of the Native American communities I have worked with, finding the best approach to roadway access management assists my clients by increasing safety while decreasing future costs. For starters, let’s take a quick look at what access management means, with respect to Tribal TTP Roadways:

Basic Definition – Access management encompasses a set of procedures that Tribes can use to control access to their roadways, which includes several techniques that are designed to increase the capacity of these roads, manage congestion and reduce crashes. The access management plan involves seeking an appropriate balance between safety and mobility within a roadway facility with the access needs of adjacent land uses.

Often, it becomes easy to overlook incorporating an access management plan into Tribal TTP transportation planning endeavors, because the results do not grab public attention unless things begin to go wrong. The following are some of the resulting pitfalls to poor access management:

Increase in crashes and crash rates;
Poor capacity;
Increased delays;
Reduces roadway efficiency;
Unwanted cut-thru traffic; and
Less desirable driving experience (less customers want to make the trip)

Luckily we have some tools and techniques to avoid these potential pitfalls. I will be adding several posts over the next couple of months addressing access management ideas. Today we will take a look at Access Spacing and how careful planning in this area can assist your Tribal TTP roadway network.

The number and types of conflict points (i.e., the number of locations where the travel paths of two different vehicles may cross) at the intersection of a driveway and a public road influence the safety of motorists. Whenever possible, minimizing the number of conflict points created with existing and future entrances is important since more conflict points increase the risk of a crash occurring.


Undesirable Intersection Spacing (FHWA image)


Desirable Intersection Spacing (FHWA image)

While it appears fairly obvious that decreasing the number of access points will reduce congestion along a roadway, safety also plays a key role. As seen in the following figure from FHWA, increasing the distance between intersections and driveways also reduces the incidence of crashes.

(FHWA image)

Because driveways and intersections are in fact inevitable on most roadways care must be given to their placement. A good practice is to avoid locating these access points on opposite sides of the roadway that creates an overlap for left turn movements.

(FHWA image)

While there are numerous additional access spacing topics to be covered, these represent the design issues I have faced more often in assisting Tribal communities with their roadway networks.

Make sure to check back here on the blog for the next access management entries, which will include discussions on Turning Lanes, Roundabouts and Dedicated Parking Lanes.