1 Longer Combination Vehicles & Road Trains for Texas? TxDOT Project CTR: Robert Harrison, Jolanda Prozzi, Kara Kockelman, Bridget Bienkowski, C.M. Walton UTSA: Angela Weissmann, Jose Weissmann Industry Panel: H-E-B, Frito-Lay, PepsiCo

Background 1982 Federal Increase 80K lb. interstate limit 14 “grandfathered” LCV states ISTEA All truck size and weight limits “frozen” Texas Trucking 59% of value 57% of the weight 44% of the miles Economy Will higher trucking costs impair growth?

LCV Adoption LCV adoption is not new—so why has it failed in the U.S? 1. Federal highways are shared—safety 2. Revenue equity issue 3. Railroads 4. Economies of scale—all modes except trucks?

Study—Texas Two truck types Key state corridors Not rail competitive Cost impacts

LCV Types Identified by Panel Source: Sunbury Transport Source: Pioneer West Double 53’ Tridem

IH20 IH37/US281 IH35 IH45 IH20/IH10 Pavement and Bridge Analysis Estimate potential LCV impacts on pavements and bridges in four Texas corridors Objective

7 Data Treatment Pavements Objective: prepare input files for the pavement analysis. 1. Divide each corridor into segments with uniform truck traffic, same pavement and same subgrade type; 2. Develop load spectra for existing and LCV scenarios; and 3. Obtain subgrade and material properties, tire pressures, detailed axle configuration.

8 152 Analysis Segments example

9 Seg 6 = 23mi Seg 4 = 7.3mi Seg 5 = 8.2mi Seg 3 = 2mi

10 LCV Scenario Existing Class 9 90k double 53’ 35% 30% 97k tridem 15% Observed spectra 138k double 53’ 20% Total cargo remains unchanged

11 Example WIM station #539 IH45 analysis segment 1 13,600 trucks /day

12 Load Spectra Analysis ADTT WIM Data Reports Analysis direction Load spectra with & without LCVs ESALs Classification counts Axle load frequencies LCV scenario Data sources Data treatment Legend

13 Tandem axles

14 Measures of LCV Impacts  life = Pvt. Life w/ LCV – Pvt. Life w/o LCV |Dlife|≥1 or Life <50yrs  cost = Annual. cost w/ LCV – Annual. cost w/o LCV  life 0  LCV scenario worse  life >1  D cost <0  LCV scenario better

15 How did we obtain  life ? Load spectra with and without LCV For the 152 analysis segments Pavement cross- sections Material and SG properties KENLAYER KENSLABS Maximum strains Maximum stress NfNf s max / S (1E6)

16 How did we obtain  cost ? No LCVs No cost analysis Life 2 Life 1 Thick HMAC overlay cost

Results

18 Recommendations Best pavement type for future LCV corridors: CRCP If flexible, analysis suggests 8” as minimum HMAC thickness to prevent premature alligator cracking. Evaluate the Dallas-Houston corridor for possible LCV operations serving the Port of Houston. Evaluate other LCV scenarios before cost allocation. Develop sensitivity analysis combining load spectra variations and different LCV scenarios for cost allocation.

Bridge Analysis

20 Bridge Statistics (1713 Bridges) HighwayCountPercent IH HighwayCountPercent IH HighwayCountPercent IH HighwayCountPercent IH HighwayCountPercent IH37845 HighwayCountPercent US

Traditional Methodology Live Load Bending Moments Proposed/Rating Ratios

Live Load Moment Ratios Inventory Rating

Case Study Configurations- 97K Tridem 97k tridem Axle Spacing: 14ft 35ft Axle Loads: 7K 34K 56K

Case Study Configurations- Double 53’ Axle Spacing: 18ft 41ft 19ft 41ft Axle Loads: 12K 31.5K 31.5K 31.5K 31.5K Axle Loads: 12K 19.5K 19.5K 19.5K 19.5K 90k double 53’ 138k double 53’

Overstress Ratios from Literature Recent designs (80s) can support 20% weight increase. Older designs susceptible to 10% weight increases. Essentially all prestressed girders, modern steel girders, and most bridge decks could tolerate a 20% increase in truck weight with no reduction in life. Unfortunately, most Minnesota steel girder bridges were designed before fatigue-design specifications were improved in the 1970’s and 1980’s. Typically, an increase in truck weight of 20% would lead to a reduction in the remaining life in these older steel bridges of up to 42% (a 10% increase would lead to a 25% reduction in fatigue life).

Moment Ratio Statistics All Routes 97K Tridem 97k tridem

Moment Ratio Statistics All Routes Double 53’ Cubed out 90k double 53’

Analysis Methodology Supported by Level 1Analysis Check if bridge deficient for existing traffic. Check if bridge is deficient for proposed LCV configuration. Record deck area and traffic volume.

Results 97K Tridem 1.1 Moment Ratio Criteria 1.2 Moment Ratio Criteria 97k tridem

Results Mixing All Configurations 1.1 Moment Ratio Criteria 1.2 Moment Ratio Criteria

Summary for all Configurations 97K Tridem: 2.8 to 1.1 billion 138K Double 53’ 1.2 to 1 billion 90K Double 53’ NO IMPACTS

Bridge Statistics – Structure Type (Preliminary Fatigue Research)

Using Fatigue Concepts (Preliminary Research) Log N = C – m Log S N – number of cycles S – Stress Range m – Constant Material dependent C – Constant AASHTO specifies 75 year design life This achievable with inventory rating stress levels. NS m =C

Using Fatigue Concepts (Preliminary Research) Assuming no influence of load spectra (equal number of passages of the proposed load): F’ Calculated bridge life due to proposed load F Current bridge life= 75-Bridge Age m material constant MAS/MBC Moment ratio from MOANSTR analysis BRINSAP Bridge Type m Prestress conrete girder [2] Prestress concrete box [2] 2. Altry, A.K., Arabbo, D.S., Crowin, E.B., Dexter, R.J. and French, C.E., (2003). “Effects of increasing truck weight on steel and prestressed bridges”, Mn/DOT final report ( ), Minnesota Department of Transportation

Results Using Fatigue Concepts (Preliminary Research) 97k tridem Discount rate 5%

Combined recommendations BRIDGES AND PAVEMENTS

Cubed-out double 53’ FINDING: “cubed-out” double 53’ has no impacts on bridges or pavements. Related recommendations Strictly enforce the 19.5K tandem weight limit (to prevent bridge impacts). Estimate and allocate the (external) cost of this enforcement in the candidate corridors. 90k

FINDING: “weighed-out” double 53’ and 97K tridem have impacts on bridges but not on pavements. 97K tridem bridge impacts are more significant. Related recommendations Develop cost-allocation / cost-recovery procedure for bridge costs. Pavement cost reductions estimated in this study too sensitive to input data variations and are not accurate enough for cost allocation. Sensitivity analysis and additional traffic mix scenarios needed. 138k and 97k

Report URL Potential Use of Longer Combination Vehicles in Texas: Second-Year Report