Geometric Design Guide for Canadian Roads

1.3.4 CHARACTERISTICS the following figure and tables. Figure 1.3.4.1 illustrates the desirable interrelationship of the OF CLASSIFICATIONS urban road classification groups. Tables 1.3.4.1 and 1.3.4.2 provide summaries of the typical The principal characteristics of each of the six characteristics of the various groups and sub- groups of road classifications are described by groups, for rural and urban roads respectively.

Figure 1.3.4.1 Relationship of Urban Road Classifications

major arterial major arterial

minor arterial

123456123456

123456collectorexpressway123456

local

freeway lane

expressway

freeway local

expressway public lane

major arterial signalized intersection

minor arterial cul-de-sac collector

January 2002 Page 1.3.4.1 Design Classification

Table 1.3.4.1 Characteristics of Rural Roads

Rural Locals Rural Collectors Rural Arterials Rural Freeways

service function traffic movement traffic movement traffic movement optimum mobility secondary and land access primary consideration of equal consideration importance

land service land access traffic movement land access no access primary and land access secondary consideration of equal consideration importance

traffic volume vehicles per day <1000 AADT <5000 AADT <12 000 AADT >8000 AADT (typically)

flow interrupted flow interrupted flow uninterrupted freeflow (grade characteristics flow except at separated) major intersections

design speed (km/h) 50 - 110 60 - 110 80 - 130 100 - 130

average running speed (km/h) (free flow 50 - 90 50 - 90 60 - 100 70 - 110 conditions)

vehicle type predominantly all types, up to all types, up to all types, up to passenger cars, 30% trucks in the 20% trucks 20% heavy light to medium 3 t to 5 t range trucks trucks and occasional heavy trucks

normal locals locals collectors arterials connections collectors collectors arterials freeways arterials freeways

Page 1.3.4.2 January 2002 Geometric Design Guide for Canadian Roads

1.4.3 OPERATING SPEED associated with different geometric elements. Limited information is generally available to CONSISTENCY assist designers with prediction of operating speeds, but the material presented in this The safety of a road is closely linked to section may help, noting the limited database variations in the speed of vehicles travelling on used. As an alternative, some jurisdictions have it. These variations are of two kinds: local data on which to base speed predictions.

1. Individual drivers vary their operating Researchers9 collected data from five US states, speeds to adjust to features encountered measuring 85th percentile operating speeds, along the road, such as intersections, under free flowing traffic conditions, on long accesses and curves in the alignment. The tangents and horizontal curves on rural two-lane greater and more frequent are the speed highways. Long tangents (250 m or more) are variations, the higher is the probability of those lengths of straight road on which a driver collision. has time to accelerate to desired speed before approaching the next curve. The mean 2. Drivers travelling substantially slower or 85th percentile speed on long tangents was faster than the average traffic speed have found to be 99.8 km/h on level terrain and a higher risk of being involved in collisions. 96.6 km/h in rolling terrain. It was noted that these speeds were probably constrained by the A designer can therefore enhance the safety of 90 km/h posted speed in force at the time. a road by producing a design which encourages operating speed uniformity. On horizontal curves, the research found consistent disparities between 85th percentile As noted in the discussion of speed profiles in speeds and inferred design speeds, with the Chapter 1.2, simple application of the design greater disparity on tighter radius curves. The speed concept does not prevent inconsistencies 85th percentile speed exceeded the design in geometric design. Traditional North American speed on a majority of curves in each 10 km/h design methods have merely ensured that all increment of design speed up to a design speed design components meet or exceed a minimum of 100 km/h. At higher design speeds, the standard, but have not necessarily ensured 85th percentile speed was lower than the design operating speed consistency between speed. components. Using regression techniques, a relationship was Practices used in Europe and Australia have found between 85th percentile speeds and the supplemented the design speed concept with characteristics of a horizontal curve. methods of identifying and quantifying geometric inconsistencies in horizontal V85 = 102.45 + 0.0037L (1.4.1) alignments of rural two-lane highways. This type – (8995 + 5.73L) / R of road typically has the most problems related to design inconsistency. These methods have Where V85 = 85th percentile not been perfected, particularly in predicting the speed on curve (km/h) performance of a newly designed road. Their effectiveness is greater in evaluating existing L = length of curve (m) roads and identifying priority improvements to reduce collision rates. R = radius of curvature (m)

1.4.3.1 Prediction of Operating 1.4.3.2 Speed Profile Model Speeds The findings outlined in Subsection 1.4.3.1 In order to establish consistency of horizontal support the conclusion that there is no strong alignment design for a proposed new road, it is relationship between design speed and necessary to predict operating speeds operating speed on horizontal curves.

January 2002 Page 1.4.3.1 Design Consistency

Consistency of horizontal alignment design The speed profile model is used to estimate the cannot therefore be assured by using design reductions in 85th percentile operating speeds speed alone. A further check can be carried out from approach tangents to horizontal curves, or by constructing a speed profile model, using between curves. Designers should note that the predicted 85th percentile operating speeds for research6,9 on which the model is based dealt new road and measured 85th percentile speeds only with two-lane rural highways. The same for existing roads. principles, however, can be applied to design of other classes of roads. For the predictive model, it is necessary to calculate the critical tangent length between 1.4.3.3 Safety curves as follows: As noted in Chapter 1.2, there is evidence that 2 − 2 − 2 = 2Vf V851 V852 (1.4.2) the risk of a collision is lowest near the average TLc 25.92 a speed of traffic and increases for vehicles travelling much faster or slower than average. While this is true in relation to the general Where: TL = critical tangent length (m) C distribution of speeds in a stream of traffic, it has also been found to apply when there is a Vf = 85th percentile desired speed on long tangents variation in speeds caused by the effects of a (km/h) reduction in speed from one geometric element to the next.

V85n = 85th percentile speed on curve n (km/h) This particular form of speed variation may be experienced in situations such as the transition a = acceleration/deceleration from a tangent to a curve, or between curves. rate, assumed to be In these cases, the previously mentioned 2 0.85 m/s research study9, found that the mean collision rate increased in direct proportion to the mean The calculation assumes that deceleration speed difference caused by the transition from begins where required, even if the beginning of one geometric element to the other. The results the curve is not yet visible. are noted in Figure 1.4.3.2.

Each tangent is then classified as one of three The numerical values from Figure 1.4.3.2 cases, as shown on Figure 1.4.3.1, by should be used with caution, because of the comparing the actual tangent length (TL) to the database used. Wherever possible, designers critical tangent length (TL ). C should use local data. However, the principles established show the effect of a lack of Having found the relationship between each horizontal alignment consistency on increasing tangent length (TL) and the critical tangent collision potential. Figure 1.4.3.2 should not be length (TL ), the equations in Table 1.4.3.1 can C interpreted to mean that collision rate decreases then be used, as appropriate, to construct the as speed decreases. speed profile model.

Page 1.4.3.2 September 1999 Geometric Design Guide for Canadian Roads 0.028 1 / Radius 2 = 0.06 m/m 0.030 max is spiral parameter in metres is superelevation

e A NC is normal cross section RC is remove adverse crownSpiral and length, superelevate L at = normal A Spiral rate parameters are minimum andFor higher 6 values lane may pavement: be above used below the the dashed dashed line line, use useA 4 4 divided lane lane road values, values having xas a 1.15. median a less single than pavement. 3.0 m wide may be treated • • • • • • • • • Notes: =0.06

max

e lane lane lane lane lane lane lane lane lane lane lane lane lane lane lane lane lane lane e AAAAAAAAAA 40 50 60 70 80 90 100 110 120 130 minR=55 0.059 50 60 908070 0.051 5060 0.054 60 50 0.060 0.056 60 65 50 0.059 0.060 60 70 50 65 60 70 min R = 90 (m) lane lan 900800700 NC600 NC500 NC400 NC350 120 RC 120300 0.023 0.024 RC 100 125250 100 90 0.025 RC 0.027 150 125 90 0.021 120 90220 150 0.028 0.030 150 0.031 140 0.023 120 140 90200 150 80 100 0.031 0.034 175 140 0.034 140 0.025 100 0.027 125 80 100 75 175180 0.037 0.034 160 0.038 0.037 150 0.029 125 100 150 80160 160 115 70 0.036 0.041 180 150 90 0.041 0.040 150 0.031 120 0.034140 140 110 80 180 70 0.042 175 0.038 85 100 0.045 175 0.043 0.034 150 115 175 0.044 75 175 125120 60 0.040 0.046 200 175 0.048 80 0.045 90 100 175 0.036 135 0.039 150 120 200 75 60 0.043 0.048100 175 110 0.048 75 0.051 175 0.047 90 0.039 160 125 175 0.051 75 175 60 135 90 0.052 200 175 0.054 0.046 0.050 70 0.049 90 120 185 0.042 150 0.045 160 70 125 200 100 0.054 200 60 125 90 0.052 70 0.057 0.052 0.049 185 90 0.043 175 140 0.055 190 0.057 200 160 65 85 0.059 100 225 195 65 0.059 110 50 0.054 125 200 85 0.046 0.055 165 0.057 0.050 190 160 225 120 0.060 100 210 65 135 85 0.056 0.060 80 110 200 65 0.051 190 160 0.060 220 0.059 0.058 0.060 215 190 85 0.060 110 235 210 0.059 125 110 90 160 220 0.054 65 75 190 0.060 0.058 220 250 125 85 110 min 220 160 0.060 90 R 125 220 0.060 0.057 220 = 70 440 110 240 min 125 250 235 R min 90 = R 0.059 min min 110 750 = 0.060 R R 600 270 = = min 250 340 250 R 250 min 0.060 = R 190 260 = 280 260 130 300 min R = 950 7000NCNCNCNCNCNCNCNCRCRC710710 500040003000 NC2000 NC1500 NC1200 NC1000 NC NC NC NC NC NC NC NC NC NC RC NC 170 NC 170 0.021 NC 175 RC 175 0.027 RC 225 200 NC 225 200 200 NC 200 RC 0.032 0.023 200 NC 250 225 200 RC 250 225 0.037 0.024 0.028 225 275 250 225 225 275 250 225 0.040 0.029 NC 0.033 RC 235 270 240 NC 235 300 275 240 0.048 NC 300 0.029 0.034 245 0.023 290 260 255 300 290 260 0.054 350 0.036 0.043 260 0.022 305 270 280 335 305 270 NC 0.058 335 0.042 0.049 280 NC 0.029 315 285 300 350 315 RC 290 350 0.049 0.055 390 0.034 330 295 400 365 335 320 365 RC 0.040 NC 380 410 380 RC 410 0.020 475 430 475 430 0.024 RC 450 495 450 RC 495 0.036 465 555 RC 465 555 515 RC 515 0.023 580 540 580 540 RC 600 600 Radius e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 Design Speed (km/h) Table 2.1.2.6 Table Superelevation and Minimum Spiral Parameters, e

January 2002 Page 2.1.2.13 Alignment and Lane Configuration / Radius 0.035 2 1 0.030 is spiral parameter in metres is superelevation = 0.08 m/m treated as a single pavement.

e A NC is normal cross section RC is remove adverse crown andSpiral superelevate length, at L normal = rate A Spiral parameters are minimum andFor higher 6 values lane may pavement: be above used thebelow dashed the line dashed use line, 4 useA lane 4 divided values, lane road values having x a 1.15. median less than 3.0 m wide may be max Notes: • • • • • • • • •

max lane lane lane lane lane lane lane lane lane lane lane lane lane lane lane lane lane lane lane AAAAAAAAAA e an 40 50 60 70 80 90 100 110 120 130 l min R = 50 0.080 50 60 908070 0.064 5560 0.067 70 5550 0.077 0.071 65 50 65 0.080 0.075 60 50 65 80 0.080 0.080 60 50 75 65 min 60 R = 120 75 min R = 80 (m) 900800700 NC600 NC500 NC400 RC350 0.021 120 100 120300 100 0.025 RC 0.026 0.030 90 0.020250 125 120 150 0.028 150 90 125 90 120 0.023220 150 150 0.031 0.034 0.035 0.039 140 0.025 90 0.027 80 140200 100 125 175 140 0.035 160 0.038 140 90 110 135180 0.030 75 175 160 100 0.042 0.045 0.048 0.039 150 0.042 0.032 0.035 150 85 105160 115 70 140 180 150 175 90 0.041 0.049 160 0.047 125 150 0.038140 180 80 70 175 110 0.050 100 0.044 0.054 0.056 165 85 0.039 0.042 165 0.051 80 125 0.053 65 125120 150 200 165 175 100 0.047 0.058 185 100 80 0.054 150 175 0.046 80 200 195 0.059 65 120 0.058 120 0.063100 0.064 175 0.051 0.046 80 100 0.049 0.057 100 175 150 0.063 135 80 160 65 200 190 0.062 200 120 0.067 200 75 120 0.055 100 165 200 0.053 0.060 220 75 220 0.069 95 125 0.067 60 0.065 140 0.071 0.073 185 0.051 0.055 75 110 190 95 0.064 160 0.061 0.072 160 190 90 75 110 225 200 210 135 0.075 55 225 125 0.068 70 0.073 185 215 0.061 240 0.069 90 235 110 0.078 160 150 110 0.080 0.77 70 200 90 0.062 0.80 0.066 0.075 125 70 0.072 175 90 0.080 190 125 235 230 220 0.074 220 110 150 220 105 0.080 160 85 0.080 200 0.076 0.072 275 250 85 270 125 0.080 0.078 65 190 250 175 125 220 0.071 0.080 85 100 0.075 160 110 0.080 200 150 250 260 250 0.080 250 min 80 175 120 R 100 min 85 = min 0.079 R 110 min 300 285 530 R 295 = R 0.080 = 230 = 250 670 0.078 390 120 min 0.080 R 95 85 = 280 min 285 280 300 R min = R 0.080 170 330 = 330 830 95 280 300 700050004000 NC3000 NC2000 NC1500 NC1200 NC1000 NC NC NC NC NC NC NC NC NC NC NC NC RC NC 170 NC 170 0.023 NC 175 RC 175 0.029 NC RC 225 200 NC 225 200 200 0.021 0.036 NC 200 255 200 0.026 NC 260 220 200 0.027 RC 0.043 225 250 225 0.032 270 250 225 225 0.032 275 NC 0.047 225 270 0.021 240 0.038 NC 300 275 240 240 0.033 NC 300 0.057 240 290 0.026 250 NC 0.040 300 290 260 280 0.042 300 0.066 260 305 0.026 260 0.050 335 305 270 310 NC 0.050 335 0.074 285 315 0.033 NC 280 0.059 350 330 285 340 NC 0.058 350 320 330 0.040 RC 0.067 365 365 295 390 365 350 400 0.047 380 NC RC 380 RC 410 410 RC 0.023 480 430 480 430 0.028 RC 450 RC 495 450 0.033 495 RC 465 0.021 555 515 465 555 515 0.026 RC 540 580 540 580 RC 0.021 600 600 RC 710 710 Radius e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 e 2 3&4 Design (Speed km/h) Table 2.1.2.7 Table Superelevation and Minimum Spiral Parameters, e

Page 2.1.2.14 January 2002 Geometric Design Guide for Canadian Roads

Figure 2.1.2.12 Lateral Clearance for Range of Lower Values of Stopping Sight Distance2

0 1 2 3 4 5 6 7 8 9 10

January 2002 Page 2.1.2.41 Alignment and Lane Configuration

Figure 2.1.2.13 Lateral Clearance for Passing Sight Distance2

Page 2.1.2.42 September 1999 Geometric Design Guide for Canadian Roads

Figure 2.1.8.3 Performance Curves for Heavy Trucks, 180 g/W, Decelerations & Accelerations7

January 2002 Page 2.1.8.5 Alignment and Lane Configuration

Figure 2.1.8.4 Performance Curves for Heavy Trucks, 200 g/W, Decelerations & Accelerations7

Page 2.1.8.6 January 2002 Geometric Design Guide for Canadian Roads and limitations. When a design is incompatible medians) are used; however the use of left-turn with the attributes of a driver, the chances for lanes was not considered effective as a collision driver error increases. Inefficient operation and countermeasure but was considered effective as collisions are often a result.3 a means of increasing capacity.8

In general, traffic volume is the most significant Cross Section contributor to intersection collisions. Typically, as traffic volumes increase, conflicts increase, Safety considerations for cross section and therefore the number of collisions increase.5 elements, such as lane width, are addressed Severity of collisions varies only slightly among in Chapter 2.2. rural, suburban and urban intersections; the percent of severe collisions is approximately 5% 2.3.1.7 Intersection Spacing higher for rural intersections.5 Considerations

Other elements related to intersection collision Both rural road and urban road network spacing rates include geometric layout and traffic is often predicated on the location of the original control.3 As previously noted, traffic control road allowances prior to urban development. measures are not addressed in this document. The systems of survey employed in the layout The relationship of specific geometric elements of original road allowances vary from region to and safety is described below: region across Canada. As rural areas urbanize, the development of major roads generally Type of Intersection occurs along these original road allowances, and consequently road networks vary from In rural settings, four-legged intersections region to region. As examples, the land survey typically have higher collision rates than system in Ontario has created a basic spacing T-intersections (three-legged) for stop and between major roads of 2.0 km, whereas the 7 signal controls. land survey system in the prairie provinces has resulted in a 1.6 km grid. In urban settings, very little difference in collision rates between four-legged and T-intersections As development occurs, this spacing is often was found for low volume intersections reduced. In areas of commercial or mixed use (Average Daily Traffic under 20 000); however, development, the traffic generated by for larger volumes, the four-legged intersection employment and retail shopping may result in 8 was found to have the higher collision rate. a reduced arterial spacing. In downtown areas, this spacing could be reduced further as Sight Distance determined by the traffic needs and the characteristics of the road network. In both an urban and a rural setting, studies have shown that the collision rate at The spacing of intersections along a road in both most intersections will generally decrease when an urban and rural setting has a large impact on sight obstructions are removed, and sight the operation, level of service, and capacity of 3 distance increased. the roadway. Ideally, intersection spacing along a road should be selected based on function, Channelization traffic volume and other considerations so that roads with the highest function will have the least In a rural environment, it was found that left- number (greatest spacing) of intersections (the turn lanes would reduce the potential of passing 9 relationship of road classification and the collisions. preferred functional hierarchy of circulation is described in Chapter 1.3 of this Guide). However, In an urban setting, it was found that multi- it is often not always possible to provide ideal vehicle collisions decrease when lane “dividers” intersection spacing, especially in an urban (raised reflectors, painted lines, barriers or

September 1999 Page 2.3.1.11 Intersections

setting. As such, the following should be On divided arterial roads, a right-in, right-out considered: intersection without a median opening may be permitted at a minimum distance of 100 m from Arterials an adjacent all-directional intersection. The distance is measured between the closest Along signalized arterial roads, it is desirable to edges of pavement of the adjacent intersecting provide spacing between signalized intersections roads. consistent with the desired traffic progression speed and signal cycle lengths. By spacing the In retrofit situations, the desired spacing of intersections uniformly based on known or intersections along an arterial is sometimes assumed running speeds and appropriate cycle compromised in consideration of other design lengths, signal progression in both directions can controls, such as, the nature of existing adjacent be achieved. Progression allows platoons of development and the associated access needs. vehicles to travel through successive intersections without stopping. For a progression Collectors speed of about 50 km/h and a cycle length of 60 s, the corresponding desired spacing between The typical minimum spacing between adjacent signalized intersections is approximately 400 m. intersections along a collector road is 60 m. As speeds increase the optimal intersection spacing increases proportionately. Further Locals information on the spacing of signalized intersections is provided in the Along local roads, the minimum spacing Subsection 2.3.1.8. between four-legged intersections is normally 60 m. Where the adjacent intersections are A typical minimum intersection spacing along three-legged a minimum spacing of 40 m is arterial roadways is 200 m, generally only acceptable. applicable in areas of intense existing development or restrictive physical controls Cross Roadway Intersection Spacing Adjacent where feasible alternatives do not exist. The to Interchanges 200 m spacing allows for minimum lengths of back to back storage for left turning vehicles at The upper half of Figure 2.3.1.6 indicates the the adjacent intersections. intersection spacing along an arterial crossing road approaching a diamond interchange. The The close spacing does not permit signal suggested minimum distance between a progression and therefore, it is normally collector road and the nearest ramp, as preferable not to signalize the intersection that measured along the arterial cross road, is interferes with progression along a major 200 m (dimension Ac on Figure 2.3.1.6). In the arterial. Intersection spacing at or near the case of an arterial/arterial cross road 200 m minimum is normally only acceptable intersection, this minimum offset distance from along minor arterials, where optimizing traffic the ramp is normally increased to 400 m mobility is not as important as along major (dimension Aa on Figure 2.3.1.6). The same arterials. dimensions apply to arterial cross roads approaching parclo-type interchanges as shown Where intersection spacing along an arterial on the lower half of Figure 2.3.1.6. does not permit an adequate level of traffic service, a number of alternatives can be Ramp Intersection Spacing at Interchanges considered to improve traffic flow. These include: conversion from two-way to one-way The upper half of Figure 2.3.1.6, as well as operation, the implementation of culs-de-sac for Figure 2.3.1.7, illustrate the suggested and minor connecting roads, and the introduction minimum intersection spacing and lane of channelization to restrict turning movements configurations on the cross road at a typical at selected intersections to right turns only. diamond interchange. The two different channelization treatments illustrate the following

Page 2.3.1.12 January 2002 Geometric Design Guide for Canadian Roads

Figure 2.3.8.6 Left-Turn Lane Designs Along Four-Lane Undivided Roadways, No Median

January 2002 Page 2.3.8.9 Intersections

Figure 2.3.8.7 Introduced Raised Median

Page 2.3.8.10 September 1999