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Super 2: Recent Research in Energy Corridors
Kay FitzpatrickSenior Research Engineer
Texas A&M Transportation Institute
Super 2 HighwaysDefinition
• Discussed in TxDOT Roadway Design Manual (Chapter 4, Section 6)
• In Texas, a “Super 2” highway is defined as a two-lane rural highway in which periodic passing lanes have been added to allow passing of slower vehicles and the dispersal of traffic platoons
Current PracticeTS2 (PL-1) – 12 [Alternating]
Current PracticeTS2 (PL-1) – 12 [Separated]
Optional 4” Dotted Extension Line
Super 2 HighwaysOperations Recommendations, 0-6135
• Eliminate use of ADT as upper limit
• ADT as tool to prioritize competing projects
• Addition of lanes preferable to added length
– Marginal benefits for >2 mi at less than 10000 ADT
– >3 mi length should be used sparingly, avoid longer than 4 mi
Measures
Value
SegmentSegment & Intersection
After crashes (actual) 40 46
Crash predicted (EB estimate) 61.7 79.3
Percent reduction 35% 42%
Statistically significant @ 95% yes yes
Super 2 HighwaysSafety Study Results, 0-6135
TxDOT 2016 Study, 0-6806
• Small effort focused on energy corridors
• Identify how heavy truck characteristics could influence roadway design guidance for rural two-lane highways
• Develop 2-pg briefing sheets on treatments
– Available at: https://static.tti.tamu.edu/tti.tamu.edu/documents/0-6806-TTI-P1.pdf
TxDOT 2016 Study, 0-6806Traffic: Field Data Collection
• Data collection in September 2016
• Four corridors with energy exploration facilities:
– Eagle Ford -- US-183 and SH 72 (w/ passing lanes)
– Permian Basin -- US-285 and SH 302 (no passing lanes)
• Components:
– Video of operations
– Spot speeds
– Site characteristics
TxDOT 2016 Study, 0-6806Traffic: Observed Spot Speeds
Sites with passing lanes, 72 and 183
– Speed difference between cars and trucks is lower
– Speed variability (standard deviation) is smaller
– Average speeds are closer to posted speed limit
40
45
50
55
60
65
70
75
80
72 D 72 U 183 D 183 U 302 D 285 D 285 U
Spee
d (
mph)
Highway, U=Up or D=Down from Recording Location
Free-Flow Vehicles
PC Truck PSL
TxDOT 2016 Study, 0-6806Super 2 Highways, Design Consistency
• TxDOT RDM provides for passing lane length:– Desirable: 1.5 – 2 mi (longer passing lanes are acceptable, but not
recommended more than 4 miles. Consider switching the direction if more than 4 miles)
• Observation: when varying passing lane lengths are used, driver expectancy is violated, therefore, consistent passing lane length is desirable
• Signing and pavement markings used to inform drivers of next passing lane
TxDOT 2016 Study, 0-6806Super 2, Review Current Practices
• Approximately 20 Super 2 corridors, primarily in south and northwest Texas
– More under construction, in PS&E, or on “wish lists”
• Corridor lengths = 12 to 69 miles
– Can span multiple counties
– Some have been extended since 0-6135
TxDOT 2016 Study, 0-6806Summary of Review via Google Earth
• Passing lane lengths vary greatly
– Generally between 0.85 mi and 1.85 mi
• Advance signing not always present
• Pavement markings
– Dotted line – observed at 7 of 20 sites
– Arrow marking – observed at 7 of 20 sites
• Saw examples of turning/speed change lanes within Super 2
TxDOT 2016 Study, 0-6806: SuggestionsDesigning Energy Corridor Treatments
• Super 2 Highways Use!
• Super 2 Passing Lane Lengths
– Room for improvements in consistency of length used
– No evidence supporting a change in desired length at this time (i.e., use 1.5 – 2 mi)
TxDOT 2016 Study, 0-6806: SuggestionsDesigning Energy Corridor Treatments
Super 2 Signing & Markings
– Room for improvements in consistency of use
– No evidence supporting changes to TS-2 other than the potential of adding an (optional) example of an end of lane arrow
– Example from Minnesota:
***place transition arrows adjacent to lane reduction signs
**** lane reduction transition arrows are optional for speeds less than 45 mph
Source: http://www.dot.state.mn.us/trafficeng/pavement/typicaldetail/passingandtransitionlanes.pdf
TxDOT 2016 Study, 0-6806: Questions for Energy Corridor Treatments
• Much is still unknown about the needs of trucks to pass on two-lane highways, particularly trucks passing other trucks
• Increasing issue: cars passing multiple trucks (platoons or convoys)
– How to handle passenger cars passing convoys of trucks?
TxDOT 2016 Study, 0-6806Closing
• Report (Tech Briefs) available at: https://static.tti.tamu.edu/tti.tamu.edu/documents/0-6806-TTI-P1.pdf
• TRB paper on “Potential Effects of Heavy Vehicles on Operations of Super 2 Highways”
• Questions:– Kay Fitzpatrick, [email protected]
– Marcus Brewer, [email protected]
– Jon Epps, [email protected]
– Bill Stockton, [email protected]
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