The level of service on two-lane rural highways can be estimated using the percent time spent following (PTSF) and average travel speed (ATS). Because PTSF cannot be directly observed in the field, the literature suggests alternative measures of service (MOS) that can be obtained from traffic stream parameters. The objective of this paper was to analyze measures of service that could adequately describe the quality of service on two-lane rural highways. Traffic data collected on 16 road segments in the state of São Paulo were used to calibrate and validate the traffic simulation software CORSIM by means of a genetic algorithm. The recalibrated CORSIM was used to create a synthetic set of traffic data that comprise an extensive range of traffic flow and road geometry patterns. Nine alternative measures of service were analyzed, and models that relate these measures of service to directional traffic flow were fitted using a synthetic traffic data set. Comparisons between the values obtained from these models and the values obtained from the field indicated that two measures of service, density and follower density, could be used to create level of service criteria for two-lane rural highways in Brazil.

Summary: The US Highway Capacity Manual (HCM) methodology is used in Spain to evaluate traffic operation and quality of service. The effect of passing manoeuvre on two‐lane highway operational performance is considered through adjustment factors to average travel speeds and percent time spent following. The procedure is largely based on simulations in TWOPAS and passing behaviours observed during US calibrations in the 1970s. It is not clear whether US driving behaviour and vehicles' performance are comparable with Spanish conditions. The objective of this research is to adapt the HCM 2010 methodology to Spanish driver behaviour, for base conditions (i.e. no passing restrictions). To do so, TWOPAS was calibrated and validated based on current Spanish passing field data. The calibration used a genetic algorithm. The case study included an ideal two‐lane highway with varying directional traffic flow rate, directional split and percentage of trucks. The updated methodology for base conditions is simpler than the current HCM 2010 and does not rely on interpolation from tables. Copyright © 2016 John Wiley & Sons, Ltd.

Four analytical models to estimate percent time spent following (PTSF) on two-lane highways were tested with data from 16 sites in Brazil. Besides percent following, the models are based on shockwave analysis, moving-bottleneck theory, or queuing theory. As direct measurement of the PTSF is impractical, PTSF values produced by a simulation program were the basis for comparison (observed PTSF values). The quality of the PTSF estimates produced by the four models was tested using 442 observations and four goodness-of-fit functions [mean normalized error (MNE), mean absolute normalized error (MANE), root-mean squared normalized error (RMSNE), and correlation coefficient $r$ ]. Although some degree of correlation between the estimated and observed PTSF values was detected, none of the four models was able to provide reliable estimates of PTSF, as indicated by high mean normalized errors (around 35%) and mean absolute normalized errors that were, on average, close to 50%.

The U.S. Highway Capacity Manual (HCM 2010) methodology is used in Spain to evaluate traffic operation and quality of service. In two-lane undivided highways, the effect of limiting where drivers could pass slower vehicles, or passing restrictions, is considered through the percentage of no-passing zones. This measure does not account for how passing opportunities are distributed along the road. The objective of this research was to evaluate the effect percentage of no-passing zones and average passing zone length on a two-lane highway and, if significant, incorporate them in the analysis methodology,. The TWOPAS microsimulation program was calibrated and validated to the Spanish conditions. Passing restrictions had little effect on average traffic speed (ATS), with differences lower than 6 km/h between a road segment with no passing restrictions and a road segment with a passing restriction on 100% of its length. Conversely, passing restrictions can increase the percent time spent following (PTSF) up to 30%. Increasing the passing zone length beyond 2,000 m does not improve PTSF. The new models could be used to better estimate traffic operation on Spanish two-lane highways.