Greater Boston’s Transportation System and Its Current Condition
A sustainable transportation system must be well maintained. Staying on Track has identified three indicators (which provide ongoing information about the system in greater Boston and Massachusetts) and one benchmark (which compares the system in greater Boston and Massachusetts to comparable peer systems) for assessing the condition of the transportation system in Massachusetts.
Indicator 4.1 Bridge Condition: Structurally Deficient Bridges
This indicator uses information from the National Bridge Inventory to track the number of bridges in Massachusetts which are classified as structurally deficient. A structurally deficient bridge is one for which the deck (riding surface), the superstructure (supports immediately beneath the riding surface), or the substructure (foundation and supporting posts and piers) is not in good condition and so the bridge has experienced deterioration significant enough to potentially reduce its load‐carrying capacity. Structural deficiency does not necessarily imply that a bridge is unsafe. The Massachusetts Department of Transportation’s Accelerated Bridge Program is working to reduce the number of structurally deficient bridges in Massachusetts and this indicator demonstrates that the state has made progress over the past three years in achieving that objective.
Benchmark 4.1 Bridge Condition: Structurally Deficient and Functionally Obsolete Bridges
This benchmark uses information from the National Bridge Inventory to compare how Massachusetts is doing compared to the U.S. as a whole and to a set of six other “peer” states that have been identified as having transportation systems that are comparable to Massachusetts. The benchmark looks at bridges that are classified either as structurally deficient or as functionally obsolete. A structurally deficient bridge is one for which the deck (riding surface), the superstructure (supports immediately beneath the riding surface), or the substructure (foundation and supporting posts and piers) is not in good condition and so the bridge has experienced deterioration significant enough to potentially reduce its load‐carrying capacity. Structural deficiency does not necessarily imply that a bridge is unsafe. Highway bridges classified as functionally obsolete are not structurally deficient, but their design is outdated. They may have lower load carrying capacity, narrower shoulders or less clearance underneath than bridges built to the current standard.
Indicator 4.2 Pavement Condition
This indicator uses information from the Massachusetts Department of Transportation to track progress on improving the quality of the pavement condition on Massachusetts highways, specifically the subset of highways that are part of the National Highway System. The National Highway System (NHS) is a system of roads identified to be of national significance including but not limited to the interstate highway system. In Massachusetts, the NHS is comprised of the entire Interstate Highway System, other major highways such as Route 3 and Route 24, and some major arterial roads such as Routes 2, 9 and 20. Of the 9,500 lane miles of roadways owned by MassDOT, approximately 6,200 are part of the National Highway System. Pavement condition data is collected and evaluated using MassDOT’s specialized testing vehicle, the Automatic Road Analyzer, or ARAN, on a biennial cycle. The ARAN measures pavement roughness, as well as indicators of pavement distress such as cracking, rutting, and raveling, and then combines them all into an overall pavement condition indicator, known as the Pavement Serviceability Index, or PSI. The Pavement Serviceability Index is measured on a five-point scale, with 0 being impassable and 5 being perfectly smooth. Based on this scale, roadway conditions are classified as poor, fair, good, or excellent. MassDOT has established a performance objective of having 80% of pavement on NHS routes classified as being in either good or excellent condition and this indicator tracks progress, or lack of progress, toward achieving that goal.
Indicator 4.3 MBTA Vehicles Beyond Useful Life
This indicator tracks the proportion of the MBTA’s overall vehicle fleet, as well as vehicles used on specific parts of the system (buses, commuter rail locomotives and coaches, Silver Line buses, and the vehicles used on each of the rapid transit lines) that is beyond the “useful life” of that vehicle as defined by the MBTA, manufacturer and/or Federal Transit Administration. The information used to calculate this indicator is taken from the MBTA’s Capital Investment Program. Because purchasing new vehicles can take many years – even after funding is identified –vehicles currently operating that are already past their useful life are likely to remain in service for many years and at risk of more frequent breakdown and failures.