Cork Institute of Technology
Bachelor of Engineering in Civil Engineering –Award (CCIVL_7_Y3)
Spring 2008 Highway Engineering
(Time: 3 Hours) Instructions: All questions carry equal marks Answer five (5) Questions – candidates must attempt all questions in SECTION A and any two (2) questions from SECTION B Attachments: (i) Table 3 from NRA TD9/00 (Road Geometry Handbook) (ii)graphs from LR1132
Examiner: Mr. D.J.Walsh Mr. P. Moran
Mr. J Lapthorne Mr. J. Kindregan
Section A Question 1 – where appropriate NRA Road Geometry Handbook standards to apply
(i) Which road classifications in the Irish road network come under the remit of the NRA?
(ii) Alignment Constraint (Ac) and Layout Constraint (Lc) are two factors used in the
assessment of what?
(iii) A single carriageway road is to have a Design Speed of 100km/hr.
What are the critical sight distances to be satisfied when designing the road?
(iv) What is meant by the terms (i) Relaxation (ii) Departure from design standards?
(v) Use a neat sketch to illustrate the geometrical cross-sectional details of a Standard
Single Carriageway. Dimension the key features of the cross section.
(vi) Cutback Bitumen and Bitumen Emulsion represent an alternative to the traditional
Penetration Grade Bitumen binder – how are they produced and what advantage do
they offer over the traditional Penetration Grade Bitumen?
(vii) The use of a Road Tar binder in-lieu of a Petroleum Bitumen Binder can be
advantageous in certain circumstances – what advantages does Road Tar offer over
Petroleum Bitumen? What are its two major disadvantages?
(viii) Which document specifies the geometric design standards required of highway
markings and signing? (Q1: 8 parts @ 2.5 marks each – 20Marks)
The minimum distance required for safe passing on two-lane single carriageway roads, i.e. the Full Overtaking Sight Distance (FOSD), has four distinct component elements - Fig. Q2 refers.
The overtaking vehicle travels a distance d1 during the perception/ reaction time and a distance d2 while completing the overtaking manoeuvre – this vehicle is assumed to accelerate from an initial speed two steps below the design speed of the road to a final speed equal to the design speed v at the completion of the overtaking manoeuvre – the acceleration a occurs over the total distance (d1+d2) and is completed in a time t seconds. (Note that the design speed steps are related by a factor of 21/4) The vehicle travelling in the opposite direction travels a closing distance d4 during this time. A safety distance d3 is provided between the vehicles on completion of the manoeuvre.
(i) Assuming a safety distance equal to 20% of the closing distance show that the Full Overtaking Sight Distance may be calculated as
FOSD = d1+d2+d3+d4 = 2.05vt where v is the design speed of the road and t is the time taken by the overtaking vehicle to travel the reaction & overtaking distance (d1+d2) (13 marks)
(ii) An assumption that 85% of overtaking manoeuvres are completed in a time t of 10
seconds has been used to generate the FOSD values specified in Table 3 of the NRA Road Geometry Handbook – verify this by comparing the FOSD value obtained using the equation derived in (i) above with the value in Table 3 for a design speed of 100km/hr. (3 marks)
(iii) (a) Illustrate how the available FOSD is measured for a given vertical road alignment
– clearly show the envelope of visibility and the relevant heights involved. (b) Explain why FOSD is not of concern to the road designer for dual carriageways.
(4 marks) (The following equations of physics may be of assistance; v = u+at and s=ut+0.5at2 ) (Q2: 20Marks)
(i) With the aid of a neat sketch identify the components of a typical horizontal alignment
curve. Identify the purpose of each of the main features of the curve. (4 marks)
(ii) Design parameter options are being considered for the horizontal alignment of a road
with a design speed of 100km/hr;
(b) For a superelevation of 2.5% what range of radii may be considered for the curve? (2)
(c) For a radius of 1200m what superelevation is required?
(1) (d) Give precise calculated details of how the superelevation of (b) will be introduced. (The recommended rate of increase of centripetal acceleration is 0.3m/s3) (2)
(iii) Gradients, both longitudinally and across a section, are critical to the effective performance of a road alignment.
What are the minimum gradients specified in the Road Geometry Handbook for both longitudinal falls and for cross-falls? Why are minimum gradients specified? (2 marks)
(iv) With the aid of a neat sketch identify the components of a typical vertical alignment
curve. What geometrical forms are usually considered for the curve and which form is the most commonly used. (4 marks)
(v) List six distinct constraints which will affect the selection of a vertical alignment
profile for a rural road scheme. Of the six, which are the two key constraints? Explain why they are key constraints. (3 marks)
(vi) List three additional constraints which may affect the selection of a vertical alignment profile for an urban road scheme. (2 marks)
(The following equations may be of assistance; L=v3/(46.7*q*R) and s=v2/2.828*R)
(i) List the principle types of priority junctions that can be applied to the junction of a major and minor roadway and briefly describe what the considerations are when deciding on the choice of junction type. (6 marks)
(ii) Describe the two main types of roundabout and list the six parameters that affect the
capacity of a normal roundabout. (8 marks)
(iii) Describe why entry deflection is so important in the design of a roundabout junction.
Outline the method by which a designer may determine entry deflection in addition to a method of achieving/improving the same. (6 marks)
(i) Approximately, how many fatalities were there on Irish roads in (a) 2005 (b) 2006 (c) 2007? (Republic of Ireland; answer to within +5 or -5 of actual figure) (3 marks) (ii) Factors which contribute to road accidents may be categorised as being either Driver
or Engineering related. (a) List five distinct Driver and five distinct Engineering issues which influence
road safety . (2.5) (b) For each issue listed write brief notes describing measures which could be
taken to improve the accident statistic rate. (5) (c) Figure 9: Two Vehicle Fatal Collisions in 2004 Classified by Contributory
Action (NRA Road Collision Facts Ireland 2004) is reproduced in Fig.Q5. For each category of Contributory Actions listed identify the Engineering solution most likely to effectively address the problem. (2.5) (10 marks)
(iii) Compare and contrast the following road cross section types in terms of potential Road Safety performance;
(a) Single Carriageway v’s Motorway Dual Carriageway (b) Standard Single Carriageway v’s Wide Single Carriageway (c) Wide Single Carriageway v’s ‘2+1’ Carriageway (7marks) (Q5: 20Marks)
Annual Average Daily Traffic and Level of Service are important parameters in Highway Engineering.
(i) (a) What, precisely, is AADT? (1)
(b) How are current AADT values derived? (1) (c) What, approximately, are the current AADT figures for the N25 at the following locations; (i) Jack Lynch Tunnel (b) Kinsale Road Interchange. (2) (d) Explain how Design AADT values are generated from current AADT values. (2) (e) Give two distinct examples of where AADT values used in the design process.
(2) (f) What Design Life period is used by the NRA for the National Road network? (1) (g) What, approximately, is the AADT capacity of a Standard Single Carriageway for a Level of Service D? (1)
(ii) A new flexible pavement is to be constructed in 2010. The AADT (2008) for the road is 25000 vehicles of which 6% comprises Heavy Goods Vehicles. The CBR value of the sub-grade is 3%. Assuming a traffic growth of rate of 3.5% and a design life requirement of 20 years design the pavement using the LR1132 design procedure – graphs/figures from LR1132 are attached. State clearly any assumptions which you need to make.
The following equations from LR1132 may be of use: Tn = 365 F0 ((1+r)n-1) / r * P D = 0.35/(0.93t+0.082) – (0.26/(0.93t+0.082) * (1.0/(3.9(F/1550)) t = (year of middle of design life – 1945)