Traffic Operations on Rural Two-Lane Highways: A Review on Performance Measures and Indicators

Abstract

Two-lane highways constitute a large proportion of the highway system in the US, particularly in rural areas. Performance evaluation on those highways is the basis for planning, upgrade and improvement programs. Such evaluations are conducted using performance measures that should ideally be correlated to performance determinants on those highways. Unlike other highway facilities, two-lane highway performance is notably affected by the platooning phenomenon, which is believed to be a function of traffic level and passing opportunities. Over the last couple of decades, several studies have addressed performance measures on two-lane highways, and are mainly driven by the reported limitations of the current measures used by the Highway Capacity Manual (HCM).

A Statistically Based Model for the Characterization of Vehicle Interactions and Vehicle Platoons Formation on Two-Lane Roads

“…It is clear that if the classification criterion is based only on the 3 s threshold, this situation of a constrained speed with a headway higher than the critical one cannot be adequately recognized and considered. Another helpful comparison can be expressed in terms of FD [18,23], expressed as the product of the percentage of non-free vehicles and the estimated flow density, the latter as the ratio between hourly flow and average speed.…”

“…Figure 13 shows the FD values, as the hourly flow varies for the entire daytime period, obtained by estimating the percentage of free vehicles over 5 min intervals, alternately using Equation ( 33) and the 3 s threshold criterion. Another helpful comparison can be expressed in terms of FD [18,23], expressed as the product of the percentage of non-free vehicles and the estimated flow density, the latter as the ratio between hourly flow and average speed.…”

“…Thus, congestion measures and performance evaluation are the basis for upgrading and improving transport programs, considering a sustainable transport system [17], namely: mobility, productivity, safety, reliability, and environmental impacts [18]. According to [18], performance measures used for traffic operations and capacity analysis on any highway facility should meet the following criteria:…”

“…The proposed methodology has been included in the Final Report for the NCHRP Project 17-65, with the recommendation to be included in the next edition of the HCM. Al Kaisy et al [18] and Washburn et al [6] highlight a panel of additional indicators for the assessment of vehicular interactions, based mainly on the concept underlying PTSF and PF; i.e., to estimate in some way the share of vehicles that are forced to travel in platoons due to the impossibility of overtaking using the opposite lane. As we refer to this study for specific insights, we must consider how these indicators, such as FD (follower density) and FF (follower flow), resort to the same assumption of a deterministic threshold value.…”

Análisis de la funcionalidad del tráfico en carreteras convencionales con presencia de ciclistas

“…El análisis realizado muestra que la presencia de ciclistas afecta a la funcionalidad del tráfico principalmente por la diferencia de velocidades entre estos usuarios y los vehículos motorizados, aumentando la necesidad de realizar adelantamientos y generando demoras en los vehículos ligeros debidas al seguimiento previo al adelantamiento. Estas demoras no afectan en exceso a la velocidad media de recorrido de los ligeros, siendo esta la medida de desempeño que se ha visto afectada en menor medida por la presencia de ciclistas en el tramo, y a pesar de ser una medida fácilmente medible en campo, presenta poca relación con la percepción de los usuarios de la carretera sobre la calidad del tráfico (Al-Kaisy et al, 2018).…”