Highway planning requires balancing access, mobility

Balancing the need for traffic movement with property access is ITD's goal in construction projects.

"Roads serve two primary purposes – to provide mobility and access. Mobility is the efficient movement of people and goods. Access is getting those people and goods to specific properties," said ITD Access Management chief Dave Szplett. "A roadway designed to maximize mobility typically does so in part by managing access to adjacent properties. Limited access is why interstate highways are so safe."

Most state highways serve a function somewhere between interstate highways, which have limited access and high mobility, and local residential roads, which provide numerous accesses to properties but are not appropriate for long-distance travel. One of ITD's most important responsibilities is to ensure the design of each state highway properly balances access and mobility. Access management is the tool used to provide that balance.

How does access management improve safety?
From 2008 through 2010, 56 percent of all crashes and 29 percent of fatal crashes on the state highway system were classified as intersection or driveway-related.

ITD access standards are designed to balance access and mobility by reducing points of traffic conflict. Conflict points are the locations on a road where two or more vehicles potentially can cross paths. At a four-way intersection, there may be as many as 32 conflict points, each of which represents the location of a possible crash.

Drivers can be overwhelmed by a large number of conflict points, increasing the potential for accidents. Good access management strives to separate conflict points by providing a reasonable distance between driveways and median openings, and restricting certain movements at some median openings.

Poor access management compromises the safety and efficiency of the highway and can result in increased crashes, commute times, vehicle emissions and fuel consumption.

Does access management impair business?
ITD recognizes the time and money investment business owners put into establishing and growing their business. Both successful businesses and a safe and efficient highway system are crucial ingredients for the economic prosperity of Idaho.

The movements that occur at driveway locations can make it difficult for through traffic to flow smoothly at desired speeds when those driveways are too closely spaced. Through access management, traffic flow becomes efficient and congestion decreases, resulting in increased exposure to roadside businesses. This also can delay the need to widen a road for several years. Even in situations where the implementation of access management creates a slightly longer route for customers to get to a business, national studies indicate that customers have no problem driving a greater distance, including negotiating U-turns, to access a “destination” business (specialty retail stores, service-oriented businesses).

In the case of “pass-by” businesses (gas stations, fast-food restaurants), studies show that as long as reasonable access is provided, access management modifications have little effect on their success.

Poor access management hinders businesses by creating congested, high-accident roadways. Closely spaced and poorly designed driveways make it more difficult for customers to enter and exit businesses safely, and access to corner businesses may be blocked by backed up traffic. Newer businesses will seek locations that have fewer access and congestion problems, and customers will patronize businesses with safer, more convenient access.

How can I be involved in planning my future access?
ITD encourages and seeks public input for roadway planning projects. Access management is always an important part of those discussions.

Opportunities to give input for projects are publicized through the news media, newspaper advertisements and direct mailings. The department encourages residents to get involved.

Anyone concerned with access management or wishing to request a new access to the state highway system can contact their ITD district office. Questions and comments are always welcome.

Published 10-21-2011