Both the New Jersey Department of Transportation (NJDOT) and the Pennsylvania Department of Transportation (PennDOT) track pavement conditions as required by federal regulations for state-maintained and National Highway System (NHS) roadways. NJDOT and PennDOT maintain data on the condition of all federal- and state-owned roadways.

States and the Federal Highway Administration use a number of different methodologies for classifying pavement conditions. A common measure of road condition is the International Roughness Index (IRI). The IRI determines pavement roughness conditions based on total inches of surface variation per mile. IRI is one of the pavement condition measurements that PennDOT uses. New Jersey integrates two condition measures, IRI and its Surface Distress Index (SDI), into condition ratings. SDI was developed by NJDOT based on the size of cracks, holes, and ruts in a roadway. Therefore, when segment miles (see below) or percentage of segment miles are added up for the region, note that these are aggregations combining two different classification methods.

Segment miles are used in the pavement conditions graphs, as both states provide data to calculate this metric. Segment miles measure the roadway length. Length is doubled for divided facilities. Unlike lane miles which fully account for pavement width, segment miles underrepresent the pavement conditions of wider roads and highways, with more lanes. About 4,200 segment miles of road are tracked in Pennsylvania and about 1,600 are tracked in New Jersey. These roads are primarily those owned and maintained by each state DOT, though they include some locally maintained roads that are a part of the National Highway System (NHS). The NHS is a federally designated network of roadways important to the nation’s economy, defense, and mobility. Section 1104 of the Moving Ahead for Progress in the 21st Century Act (MAP-21) expanded the NH) by including all principal arterials in existence on October 1, 2012. adding 60,000 miles to the NHS. This is the reason for the increase in NHS segment miles in 2013 in the charts below, along with the decrease in non-NHS segment miles.