By Mike Spack, PE, PTOE
Driving is a means to an end. People overwhelmingly choose to drive their cars to get somewhere – to work, the grocery store, home, daycare, the movie theater, etc. Developers are in the business of building these destinations. They need to get people into their developments for the developments to thrive, whether they are office buildings, retailers or subdivisions.
The structures have doors for people to walk through, which may be enough access if the development is downtown or at a light rail station where everyone is arriving on foot via transit. Most of the time, however, developments need driveways so patrons can park at the destinations. For large developments, developers may need to build public streets so cars can get to the driveways. On really large projects, like the Mall of America, they may need a freeway interchange so people can ultimately get to the driveways.
All successful developers have learned that access is very important for a good project. A healthy development includes convenient access. The value of raw land is dependent on the convenience of its access.
So if driving is a means to an end, why don’t government agencies let developers build driveways wherever people want to go?
Agencies used to be pretty loose with letting driveways go in wherever they were wanted. A good example was Highway 169 in Belle Plaine, Minnesota. Businesses had hundred-foot-long driveways to get cars in and out wherever they wanted. These expansive driveways led to cars cutting in front of each other, which led to a lot of crashes. In the 1990’s, those long driveways were combined, narrowed or closed on Highway 169 to limit the places cars could cut in front of each other as a way to make the road safer. The city was working on an interchange plan to convert Highway 169 to a freeway with no direct access. Creative traffic engineers call this access management.
Access management history
The concept of access management is not a recent invention. It is a concept that’s been evolving since the 1870s. In the first part of the 20th century, American cities started building boulevards patterned after those in Paris. The Minneapolis parkway system designed by Frederick Law Olmsted is a good example of the boulevard system with limited cross streets and direct access.
From about 1910 to 1940, we saw the rise of parkways like Lilac Way (Highway 100). The parkways had even less access than the boulevards. These were the first thoroughfares built exclusively to move automobiles. They were the precursor to the modern highways, freeways, and interstates. After World War II, we moved into the era of freeways to be able to move our military quickly across the country, which provides the ultimate in access management.
Planning roadway systems with limited access matured along with the construction of the suburbs. In 1954, one of the first instances of no direct left turns into a development was built at the Northland Shopping Center in Detroit. In 1962, Herbert Levinson took access planning to a citywide level in his paper Operational Measures-Future. In it, he described how major street intersections should be located at half-mile intervals with minor access intersections placed at quarter-mile points. Spacing traffic signals at quarter-mile intervals allowed traffic to move progressively through the traffic signals at 25 to 30 mph with the signal technology of the day.
During the 1980s, several states developed access management policies. According to Access Management: Past, Present, and Future, July 14, 2008, by Williams and Levinson, these systems had five common features:
- An access classification system that builds upon the roadway functional classification system
- Permitted access for each access class
- Signalized and unsignalized access spacing
- Means of enforcement
- Provisions for variance
Current access management practice
Key to access management is a system of complimentary roadways that provide varying degrees of access, from local streets with driveways 75 feet apart to freeways with interchanges every half mile to two miles. In between are collectors (county roads or city streets) and minor arterials (typically county roads). Collector streets provide mobility for people to get out of neighborhoods and have fewer driveways than local streets. Minor arterials get people across town or to a freeway interchange.
According to the Transportation Research Board’s Access Management Manual, “an effective access management program can reduce crashes as a much as 50 percent, increase roadway capacity by 23 to 45 percent, and reduce travel time and delay as much as 40 to 60 percent.” These public benefits have led planners and engineers to develop comprehensive transportation plans for their jurisdictions. MnDOT, the Metropolitan Council, counties and most cities have them now. These plans are usually a subset of the agency’s Comprehensive Plan.
The Transportation Research Board’s Access Management Manual provides the following model access spacing guidelines:
Example of Guidelines for Access Spacing (ft) on Suburban Roads
|Functional Class of Roadway||Undivided Roadway||Full Median Opening||Right In/Out Only||Directional Median Opening|
|Strategic arterial||Not applicable||2640||Typically not permitted|
|Collector||330||Not applicable, medians typically not used|
Source: Transportation Research Board’s Access Management Manual, Table 9-11
Each jurisdiction has taken these guidelines and modified them for their use — some more conservative and some more liberal.
Economic impacts of access management
Iowa State University did a series of case studies on the effects of access management on safety, traffic operations and business vitality. In most instances, they found business improved in access-managed corridors because motorists found the 15-minute drive to the development was better, even if it took them 30 extra seconds to get into the development. The economic findings from the Access Management Research and Awareness Program Phase IV Final Report were:
- Access managed corridors generally had lower rates of business turnover than other parts of their communities.
- They had more rapid growth in retail sales once projects were completed.
- Far more business owners, when surveyed, indicated that their sales had been stable or increased following project completion than reported sales losses.
These were interesting findings, but that was Iowa and this is Minnesota. MnDOT was curious to see if the same business conclusions held in Minnesota. They hired a local consultant and Iowa State University’s Center for Transportation Research and Education to perform a study of one of the biggest access management projects in Minnesota history – the conversion of Highway 12 to Interstate 394.
They found even though traffic has doubled along the I-394 corridor since its conversion to a freeway in 1993, fatal crashes were cut in half and travel times are two to 25 miles per hour faster (depending on the segment). From a traffic engineering perspective, the conversion was a clear success.
The business impacts aren’t quite as clear-cut. There were a few specific businesses harmed by the limited access. However, there were no trends that showed all businesses in a specific category were hurt. (For instance, some restaurants suffered while others thrived). The major conclusions regarding the business impacts of the I-394 Corridor Study are:
- Converting US 12 to I-394 supported economic development and improved the vitality of the corridor. Land values increased, employment increased, there are few vacant parcels in the corridor, and business turnover, while not zero, is less than the statewide average.
- These results are remarkably similar to those reported in the literature in other studies (Kansas, Texas, Iowa, and Florida).
- The success or failure of individual businesses appears to be more related to the ability of the owner to adapt to changes in the global, national, regional, state and local economies, than to the micro-level changes in accessibility.
Does all of this data mean there is no bending in the access management guidelines jurisdictions have adopted in their transportation plans? Not quite. Dakota County was an early adopter of access management and is a national leader in the area.
However, Kristi Sebastian, Dakota County traffic engineer, detailed in her presentation Implementing Dakota County’s Access Management Plan a case where access was granted on an interim basis from Cedar Avenue and Dodd Boulevard, even though the development driveways did not meet the county’s access spacing guidelines.
The direct access will be removed per the developer’s agreements when alternate access can be provided by future frontage roads, which has since happened.
Most jurisdictions are open to discussing variances as long as there is clear engineering analysis that justifies a variance. Like the Dakota County case, the variances are typically granted on an interim basis and the agency has the clear right to remove the access when alternate access is provided.
Creative engineering can also help find a solution that will work in the long term. Roundabouts offer better operations of closely spaced intersections than traffic signal control. We’ve succeeded in demonstrating closer access spacing will work by utilizing roundabouts and other means of access control.
The safety, traffic operations and business operations benefits of following access management is clear right now. We recommend developers factor access spacing requirements into their projects. Don’t pay a premium for land assuming that you can get a variance, because the days of direct access for every parcel are over. If you have a question about access spacing call us or your local traffic engineer to discuss access before you execute the land purchase.
Caveat — Access management strategies are our industry’s current best practice. Autonomous vehicles will provide exponential gains in safety and mobility while lessening the need for access management.
For more information on access management, check out theese articles and videos: