Highway Construction Services
Amherst Street Evaluation Report
107 Perrin Drive Fall River, Nova Scotia B2T 1J6
Introduction Highway Construction Services (HCS) was directed to evaluate the street network belonging to the town of Amherst. Once the network evaluation was completed a rehabilitation and preservation work program was to be developed. The evaluation and work program development was conducted in a manner in keeping with the process used by HCS to evaluate and select treatments for the provincial road network.
Evaluation and Program Development Process The street network distress evaluation process was completed by HCS staff. This process involved evaluating a network comprised of 183 asphalt paved road segments. Gravel roads were not considered as part of this review. Staff visited each road in the network and visually inspected the road and detailed the pavement surface distresses. The severity and density of the distresses were recorded on a flexible pavement condition evaluation form and were used to determine the distress manifestation index (DMI) of each street. The DMI reports for each street are attached to this memo for reference. This process is detailed in NSTIR’s Flexible Pavement Evaluation Guide. A DMI of 0 represents a newly paved street segment in perfect condition and a DMI of 100 represents a completely deteriorated unserviceable street segment. HCS Inspector Specialists, when able, used dashboard mounted cameras to collect images of each street in the network. A simple database was created containing each street in the town of Amherst’s network, lengths, widths and pavement types. The DMI for each street was added to this spreadsheet for each street segment. An approximate back-calculated present age was determined using deterioration equations obtained from NSTIR’s highway pavement management application. In order for this calculation to be successful a default last treatment had to be assumed for each street. HCS staff decided to assume that the last treatment performed was a single lift asphalt overlay. A chart illustrating the DMI curve for a single lift overlay using NSTIR’s deterioration equation is included for reference (Figure 1). The DMI and assumed default treatment allowed for a preservation and rehabilitation need year to be determined. The trigger value used for preservation was a DMI of 40 and for rehabilitation a DMI of 60 was used. Street segments that had already exceeded target values triggered immediately, while some sections that were still in good condition deteriorated over time until they met or exceeded the trigger values for preservation or rehabilitation.
Single Lift Overlay DMI Curve
60 50 40 30 20 10 0 0
Years Figure 1 - Distress Manifestation Curve for Single Lift Overlay Treatment
The next step involved building a work program for the street network. The initial conditions for this analysis were: no budget constraints (annual or evaluation period) and report work needed in sub-totals for time periods of zero to five and six to ten years. NSTIR’s ‘seal coat type A’ (single chip seal) was chosen to be the preservation treatment and, depending on adjacent curb/gutter conditions, a single lift asphalt overlay or mill and single overlay were chosen to be the rehabilitation treatments. Each treatment
was determined based on the streets current condition and time until deterioration to reach or exceed each trigger value. As no budget constraints were known, when the trigger year was met, a treatment was automatically applied. Once the treatment was applied in the need year the street was then deteriorated along the appropriate deterioration curve (Seal Coat Ty