HIGHWAY AND TRAFFIC DESIGN

Highway and traffic design using (Autocad)



Highway and traffic design using (Autocad)

Introduction

The recently developed guide for the “Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures” (commonly referred to as the M-E Design Guide) proposes applying mechanistic principles to replace the traditional empirical design approach suggested in the AASHTO 1993 “Guide for the Design of Pavement Structures.” One of the most significant improvements offered in the M-E Design Guide is the methodology to account for highway traffic volumes and loads. This enhancement proposes replacing the number of equivalent single axle loads (ESALs) by using actual axle load distributions per axle type per vehicle class. These distributions are often referred to as axle load spectra. The main goal of this research was to assess and address the implications of the axle load spectra methodology proposed by the M-E Design Guide (Hearnshaw, 2004, 33).

Discussion and Analysis

In addition, recommendations were developed regarding traffic data needs and availability. A methodology was also developed for specifying accuracy of WIM equipment based on the effect that this accuracy has on pavement performance prediction. Through rigorous statistical analyses, it was determined that the use of continuous distribution functions offers numerous advantages in comparison with the proposed discrete axle load spectra. Associated with these statistical analyses, the use of moment statistics was evaluated and was found to be the best summary statistics to characterize axle load spectra from the view point of load-associated pavement damage.

Regarding traffic volume variability forecasting, a methodology was developed that allows optimum use of available data by simultaneously estimating traffic growth and seasonal traffic variability. The research study evaluated the current version of the M-E Design Guide and determined the traffic data needs. Traffic data provided by the Texas Department of Transportation's (TxDOT) Transportation Planning and Programming Division (TPP) was processed and used to conduct a pavement evaluation and sensitivity analysis. The findings of the sensitivity analysis were used to quantify the effect of various traffic variables on pavement design and performance.

CAD, vector-based GIS, and drawing software share many concepts that make it relatively easy for users to move back and forth among systems. Phenomena are represented graphically as points, lines, and areas/shapes. Features of particular types (e.g., roads, streams, or census boundaries) are organized into common layers or levels. All the systems offer tremendous flexibility in how the data are symbolized, for example, by hue, value, texture, size, orientation, and shape. Principles of effective cartographic and visual symbolization and display apply just as strongly to CAD systems as they do to GIS and drawing software.

A gap analysis between needs and available data in Texas was performed. Based on this analysis, recommendations for temporal and spatial distribution of weigh-in-motion (WIM) stations were developed. In addition to running the mechanistic pavement analysis, the research team conducted rigorous statistical analyses of the traffic data sources available in Texas. These sources included data from TxDOT's network of permanent WIM stations and traffic volume data contained in TPP's TLOG database (Jones, 2007, ...