United States Department of Transportation
i
Validating the National Performance Management Research Data Set (NPMRDS) for South Dakota
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2018-03-01
[PDF-2.24 MB]
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Abstract:The Texas A&M Transportation Institute (TTI) evaluated the accuracy, temporal completeness, and geographic coverage of NPMRDS in South Dakota to determine whether the South Dakota Department of Transportation (SDDOT) should use the National Performance Measure Research Data Set (NPMRDS) for the federal performance management measure regulations as well as other internal applications. TTI found that speed errors were significantly higher on lower-volume arterial roads than on higher-volume Interstate highways. Also, the NPMRDS free-flow speeds are biased low in all cases (e.g., NPMRDS free-flow speeds are 7 to 9 miles per hour (mph) slower than SDDOT-reported free-flow speeds). For all-vehicle travel times, Interstate roads are typically 90% complete during daytime hours (defined as 6 am to 8 pm), and non-Interstate National Highway System (NHS) roads are typically 35% complete during daytime hours. For truck-only travel times, Interstate NHS roads are typically 80% complete during daytime hours, and non-Interstate NHS roads are typically less than 20% complete during daytime hours. The geographic coverage of NPMRDS in South Dakota matched the NHS network within 1% of expected total statewide mileage. Based on these findings, TTI recommends that SDDOT use NPMRDS to meet the Federal Highway Administration (FHWA) requirements, but should set conservative targets that acknowledge the limitations of NPMRDS on low-volume non-Interstate NHS roads. On Interstate highways and higher-volume roads (i.e., greater than 5,000 Average Annual Daily Traffic (AADT)), SDDOT can use NPMRDS for several internal uses. Caution should be used with NPMRDS free-flow speeds, as these free-flow speeds tend to be at least 5 mph slower than speeds measured at SDDOT monitoring sites. On non-Interstate NHS roads and low-volume roads (i.e., less than 5,000 AADT), SDDOT should use caution when considering NPMRDS data, and may consider internal uses on a case-by-case basis. When possible, NPMRDS data on low-volume roads should be aggregated over multiple days, weeks, or months to increase the sample size and the consistency of the speed data.
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