• Journal of Construction Engineering and Project Management
• /
• v.4 no.1
• /
• pp.15-28
• /
• 2014

Completing road construction projects within the budget and time has been a problem for the Tanzania National Roads Agency (TANROADS); and the major problem highlighted in almost all projects being inadequate design. However, the extent to which inadequate design contributes to both time and cost overruns and its causes remained under-studied. The objective of this study is therefore to determine the extent of the effect of inadequate design, its causes and remedial measures. The methodology used in this study includes reviewing recent projects completion reports, holding roundtable discussions with consultants and TANROADS officials and analyzing the information. Cost and time overruns for the reviewed projects averaged 44% and 26% respectively. Similarly, the extents to which inadequate design contributes to cost and time overruns were on average found to be 61% and 85% respectively. The overruns are predominantly related to problems that occurred during the design process. To alleviate the problem, TANROADS is advised to improve the management of design projects, enhance the process of reviewing design reports, improve the design process including introducing Road Safety Audit and geometric design manuals, and increase staff to match the work-load.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.14 no.4
• /
• pp.375-395
• /
• 2012

According to the local highway tunnel ventilation guideline, ventilation capacity calculation should be performed at the speed ranging from 10 km/h to 80 km/h. This is so reasonable method considering uncongested and congested traffic conditions in urban tunnels. But recently due to low traffic volume and very low congestion frequency in rural highway tunnels, it seems to be an inadequate way to apply the guideline. Therefore the calculation should be performed separately for the free flow and congested traffic cases classified by the appropriate decision model. This paper aims at determining unnecessary running speed range for reasonable tunnel ventilation design, considering free flow and congested traffic conditions. Firstly, traffic volumes in highway tunnels were collected and if any, the causes of congestion were investigated. And with concept of 'margin speed'($u-u_m$), the decision model on traffic congestion was developed. Applicability of the decision model was also analyzed with case study. According to the results, when design speed is 100 km/h, with V/C less than 0.1, then the range of unnecessary speed in tunnel ventilation design is less than 40 km/h; for $V/C{\leqq}0.35$, $V/C{\leqq}0.6$ and $V/C{\leqq}0.75$, the unnecessary speed ranges are found to be ${\leqq}30$, ${\leqq}20$ and ${\leqq}10km/h$, respectively.

• International Journal of Highway Engineering
• /
• v.10 no.2
• /
• pp.1-13
• /
• 2008

This study presents a case study of condition evaluation of various asphalt pavement sections to estimate performance lives. The pavement surface conditions including cracking and rutting are first evaluated using a automatic pavement analyzer, ARAN. HPCI(Highway Pavement Condition Index) values are estimated using the pavement surface distress data. It is observed from the pavement distress survey that the major distress type of the sections is top-down cracking. The modulus value of each pavement layer is back-calculated from the defection data obtained from a FWD(Falling Weight Deflectometer) and compared with the laboratory measured dynamic modulus values. Remaining lives of the various pavement sections are estimated based on a mechanistic-empirical approach and AAHTO 1993 design guide. The structural capacities of the all pavement sections based on the two approaches are strong enough to maintain the pavement sections for the rest of design life. Since the major distress type is top-down cracking, the remaining lives of the pavement sections are estimated based on HPCI and existing performance database of highway pavements. To evaluate the causes of premature pavement distress, various material properties, such as air void, asphalt binder content, aggregate gradation, dynamic modulus and fatigue resistance, are measured from the field cores. It is impossible to accurately estimate the binder contents of field samples using the ignition method. It is concluded from the laboratory tests that the premature top down cracking is mainly due to insufficient compaction and inadequate aggregate gradation.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.13 no.4
• /
• pp.138-147
• /
• 2010

As inaccurate traffic volume prediction may result in inadequate transportation planning and design, traffic volume prediction based on traffic volume data is very important in spatial decision making processes such as transportation planning and operation. In order to improve the accuracy of traffic volume prediction, recent studies are using the geostatistical approach called kriging and according to their reports, the method shows high predictability compared to conventional methods. Thus, this study estimated traffic volume data for St. Louis in the State of Missouri, USA using the kriging method, and tested its accuracy by comparing the estimates with actual measurements. In addition, we suggested a new method for enhancing the accuracy of prediction by the kriging method. In the new method, we estimated traffic volume data: first, by applying anisotropy, which is a characteristic of traffic volume data appearing in determining variogram factors; and second, by performing co-kriging analysis using interstate highway, which is in a high spatial correlation with traffic volume data, as a secondary variable. According to the results of the analysis, the analysis applying anisotropy showed higher accuracy than the kriging method, and co-kriging performed on the application of anisotropy produced the most accurate estimates.