Travel Time Reliability Reference Manual/Surface Plots of non-recurring events
TTRMS analysis tool provides numerous important surface plots that display individual records throughout an entire year for each corridor. This makes the plots more accurate and easier to compare with surface plots from other years and corridors. For all of the surface plots shown in this section, each day of the year is shown across the x-axis from left to right. The time of day is shown on the y-axis from bottom to top and is split into five-minute time intervals.
Surface plots were prepared for all of the data elements included in the travel time reliability monitoring system (TTRMS) database. These can broadly be categorized in two groups: one is the traffic data, which is continuous and includes the aggregate measures of vehicle miles travelled (VMT) and travel time. The other is the non-recurring conditions data. These records are not necessarily continuous as there are times when none of these conditions are present on the corridor. The non-recurring conditions include:
• Weather
• Crash
• Incident
• Road Work
• Event
Figure 1 and Figure 2 are examples of the surface plot for the crashes and incidents in 2012 along the I-94 Westbound from I-494 to TH 101. Crash and incident information was gathered from three different sources, which include:
• Minnesota State Patrol Computer Aided Dispatch (CAD) data
• MnDOT’s Dynamic Message Sign (DMS) logs
• Minnesota Department of Public Safety (DPS) crash records.
Crash plots are color coded by crash severity. Incident plots are color coded by impact to roadway capacity.
Figure 1: 2012 WB I-94 Crash Surface Plot
Figure 2: 2012 WB I-94 incident Surface Plot
Figure 3 is an weather surface plot example that shows the weather data collected at the Weather Underground site near the I-94 study corridor in 2012. The colors in the legend represent the precipitation type.
Figure 3: 2012 WB I-94 Weather Surface Plot
Figure 4 is an event surface plot example. The majority of the events considered in this analysis take place during or after the p.m. peak period. Therefore, events have a greater impact on the corridors where the traffic volume is highest during the p.m. peak period.
Figure 4: 2012 WB I-94 Event Surface Plot