Roadside Clearance Limit on Horizontal Curves with Transition Arcs

Mauga, Timur; Ghanma, Mwafag; Ahmed, Kamran

doi:10.3141/2358-03

Cited by 9 publications

(6 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Simple curves are the focus in this paper because many agencies do not use spiral transitions. The model for horizontal curves with spiral transitions is found elsewhere (16). The secondary objective is to derive design aids from the analytical model for use by practitioners.…”

Section: Et Al (4) Develop a Straightforward Quadratic Relationship Between Offsets And Location As Presented Bymentioning

confidence: 99%

Horizontal Clearance Offsets to Objects Higher than Sight Lines

Mauga

2014

Transportation Research Record

Self Cite

View full text Add to dashboard Cite

Sight distance is an important design element of curved highway sections. To ensure that design sight distance is provided on curved sections, AASHTO guidelines require that the insides of horizontal curves be cleared of sight obstructions. However, the guidelines’ analytical method for determining the extent of clearance is suitable only for the middle sections of horizontal curves that are longer than sight distance. The guidelines suggest the use of computational or graphical methods for determining the clearance offsets for cases in which the AASHTO model is inapplicable. The computational method is useful only for curves that are longer than sight distance but have unknown analytical aspects. The graphical method works for all lengths of horizontal curves but is tedious, time-consuming, and outdated. An analytical model for the determination of horizontal clearance offsets for sections that are not covered by the AASHTO model was developed and verified. The offsets were derived as ordinates from driver path to a roadside curve that acts as a boundary for the area that accommodates sight lines. Main factors in the equations were driver location, sight distance, curve radius, and curve length. With the use of the analytical model, a new design chart was developed for use by practitioners on both short and long simple curves. These results have dual applications: for controlling the proximity of high objects to highways and for input into research on the acceptable heights of roadside objects (e.g., safety barriers) so that they do not block sight distance.

show abstract

Section: Et Al (4) Develop a Straightforward Quadratic Relationship Between Offsets And Location As Presented Bymentioning

confidence: 99%

Horizontal Clearance Offsets to Objects Higher than Sight Lines

Mauga

2014

Transportation Research Record

Self Cite

View full text Add to dashboard Cite

show abstract

“…The angle of deflection of a sightline from the approach tangent is given by Equation (18). Equation (18) was obtained in the similar way that of case 1(c) was.…”

Section: Case 2(c): Driver On the Curve And Object On The Receding Tamentioning

confidence: 94%

“…Such lengths of reverse tangents result in the component curves being almost isolated or fully isolated. Agencies that use spirals for transitioning turning on horizontal curves may find related clearance offsets in another work [18].…”

Section: Cosmentioning

confidence: 95%

New Spiral Curves for Appropriate Transition of Minimum Roadside Clearance on Simple Curves

Mauga¹

2015

JTTs

Self Cite

View full text Add to dashboard Cite

Guidelines for geometric design of highways require that the inside of horizontal curves be cleared of obstructions to sight in order to provide necessary sight distance. Many of these guidelines use one analytical model for determining minimum clearance offsets. These offsets are suitable for middle sections of long curves because the analytical model was derived with consideration that drivers on the curves are able to see downstream curved sections whose lengths are equal to stopping sight distance. Applying these offsets to straight sections near beginnings and ends of the curves results in unnecessary clearance costs since sightlines are accommodated within lanes and wide shoulders. This paper presents a new analytical model for gradual transition of clearance from zero on straight sections to the minimum value required at the middle of horizontal curves. The model is based on new spiral curves whose mathematical equations incorporate driver location, object location, radius of horizontal curve, length of horizontal curve, and design sight distance. Moreover, the already known Euler's spiral curve is examined whether or not it is also suitable for transitioning clearance. It is found that the Euler's spiral consistently underestimates clearance offsets. Underestimation of the offsets is due to high degree of sharpness of the Euler's spiral which renders the spiral unsuitable for transitioning clearance. Finally, the analytical model is presented in the form of a design chart. Without compromising safety and mobility of highways, use of either the design chart or the analytical equations will help agencies save money that would otherwise be spent for unnecessary extra clearance of roadside areas near beginnings and ends of horizontal curves.

show abstract

“…Otherwise, the results will be approximate and it would be advisable, according to these guidelines, to check the design by a graphical procedure or a computational method. Mauga et al [8] reported the difficulties inherent to the use of these graphical methods and proposed a fully analytical model for determining the clearance boundary on a horizontal curve. Lovell [9] devised a method for automatic computation of ASD subject to constraints of horizontal geometry where precise information of sight obstructions is not available.…”

Section: Introductionmentioning

confidence: 99%

Reliability-Based Analysis of Sight Distance Modelling for Traffic Safety

Santos-Berbel

Essa

Sayed

et al. 2017

Journal of Advanced Transportation

View full text Add to dashboard Cite

Sight distance is of the utmost importance for traffic safety. The consideration of three-dimensional (3D) available sight distance (ASD) in geometric design has been supported by several researchers. However, existing ASD estimation methods are two-dimensional (2D) in nature, which do not evaluate varying visibility conditions. This paper compares different methodologies of modelling the ASD. The ASD of 402 horizontal curves, located in twelve in-service two-lane rural highways, was analyzed. Three ASD estimation methods were used which include a 2D method and two different 3D methods. The ASD results obtained through 2D and 3D methodologies are compared. Also, the different conditions of the existing roadside features or geometric elements, under which the 3D ASD estimation is important, were identified. Next, reliability theory is utilized to evaluate the risk level (probability of noncompliance,Pnc) associated with limited sight distance for each ASD modelling method. The results of the comparison emphasized the importance of considering the 3D modelled sight distance when evaluating the associated risk either in highway design or during the service life. In addition, the results indicated that the ASD modelling approach can have a significant impact on the estimation of the safety of highway design.

show abstract

Roadside Clearance Limit on Horizontal Curves with Transition Arcs

Cited by 9 publications

References 7 publications

Horizontal Clearance Offsets to Objects Higher than Sight Lines

Horizontal Clearance Offsets to Objects Higher than Sight Lines

New Spiral Curves for Appropriate Transition of Minimum Roadside Clearance on Simple Curves

Reliability-Based Analysis of Sight Distance Modelling for Traffic Safety

Contact Info

Product

Resources

About