Broomfield has redesigned its standards and specifications to include performance specifications before new streets are accepted. Here’s why – and how it works.

by Gene Putman, P.E. and Dennis Polhill, P.E.

Broomfield is a city of 24,945 people located midway between Denver and Boulder. Because of its location, it has grown from a community of 7,000 in 1970. Broomfield ,is affected by the numerous urgent issues typical of boom cities.

The city accepts approximately eight miles of new streets from various developers each year. The soil is primarily clay. typical of front range cities, and is a poor foundation for all types of structures. With limited staff resources to monitor street construction, city engineer Gene Putnam proposed a modification to the city standards and specifications.

Reviewing standards

In 1982 and 1983, the city’s engineering department began a thorough review of the existing city standards and specifications. This review determined which requirements worked properly and where problems in the field suggested a need for changes to the Standards and Specifications. The review and rewrite of the Standards took 24 months to complete, including working with other city departments and reviewing the standards and specifications of other cities in the Denver metro area.

Broomfield’s streets were not performing as required by design. The city’s original pavement section in residential areas was two inches of asphalt and six inches of base. This was changed to three inches of asphalt on eight inches of base as a minimum standard.

The city standards were also changed to require that, during the construction of a residential street, the entire pavement section must be installed with the exception of the final one-inch of asphalt. This final inch would remain oft until the construction of the majority of homes in that area is completed. The reason for the requirement is that, during the construction period, the construction traffic (concrete trucks, material haulers, cranes. etc.) is heavier than normal residential traffic would be. It is unreasonable to require the street design to accommodate this heavier loading, since it exists only at the beginning of construction and not during the normal life of the street.

Before the last inch of asphalt is applied, a new city specification requires that testing be performed to check the adequacy of the existing pavement and what additional asphalt overlay is required to bring the street into conformance.

Deflection testing

The new specification requires the use of non-destructive deflection testing to evaluate the adequacy of pavements. The evaluation is performed by the developer at the time that acceptance is requested. The city requires that the evaluation use a 10-year design life and that the deflections be analyzed by a registered professional engineer with demonstrated experience in the pavement evaluation field. The design life criteria requires that minimal maintenance will be required over the 10-year life.

The application of deflection technology is fairly new. In simple terms, the pavement gets weaker each time it deflects. The pavement deflects each time a load passes over it. The rate at which cracking, distortion, and other irregularities appear is dependent upon the pavement strength. The amount of pavement strength can be measured by measuring how much the pavement deflects under a known load and load application procedure.

Specification accepted

The new standard was adopted September 1984, with some apprehension on the part of both city council and developers. The apprehension increased when the first development evaluated showed serious deficiencies. The apprehension ceased, however, when another development proved acceptable. The standard is now solidly endorsed by all parties – council, developers, city management, and city engineering.

Without the performance specification. Broomfield would have accepted the streets in the first acceptance request and would have been burdened with excessive maintenance costs and a poor service level until capital expenditures could have been budgeted for major rehabilitation. Because the deficiencies were identified prior to pavement failure, the developer was able to make repairs to the roadway before applying the final lift of asphalt.

At first the development community was concerned about the extra cost. However, the credibility level of the more conscientious developers has increased, and even the developers are happy with the new standard. Now they can sell homes with a virtual guarantee that the street will be in good condition for a period of time. Home buyers also have the assurance that disputes over street maintenance responsibility between the city and the developer are not likely to occur.

Other communities in front range Colorado have followed Broomfield’s lead. Several communities have conducted performance evaluations on an individual project basis. Littleton and Arapahoe County have adopted the Broomfield specification for all street acceptances.

For a copy of the Broomfield performance specification, contact Gene Putman at 303-469-3301, or Dennis Polhill, Pavement Management Systems, Inc., at 303-232-2207.

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