10. Design Considerations

10.1 Clearance Distance (cd)

10.1.1  Clearance Distance (cd) is the distance between the clearance point in advance of the grade crossing, to the clearance point beyond the farthest rail, as shown in Figure 10-1. 

10.1.2  The clearance point is the point 2.4 m beyond the outside edge of the farthest rail from the departure point measured perpendicular to the rail.

10.2 Vehicle Travel Distance (S)

10.2.1  The total distance, in metres, the design vehicle must travel during acceleration to pass completely through the Clearance Distance (cd) is calculated using the following formula: 

S = cd + L   equation 10.2

where,

cd = Clearance Distance in metres; and

L = the total length, in metres of the design vehicle.

Figure 10-1 – Clearance Distance (cd) for Grade Crossings

(a) For Grade Crossings with a Warning System or Railway Crossing Sign

 text version of image below

Text version of Figure 10-1 a)

(b) For Grade Crossings without a Warning System or Railway Crossing Sign

 text version of image below

Text version of Figure 10-1 b)

10.3 Departure Time - General

10.3.1  The Departure Time is the greater of the time required for the design vehicle to pass completely through the Clearance Distance (cd) from a stopped position (TD) or the time required for pedestrians, cyclists and persons using assistive devices to pass completely through the Clearance Distance (cd) (TP).

Table 10-1 Ratios of Acceleration Times on Grades must be used to account for the effects of road gradient on the design vehicle for the grade crossing.  The established ratio of acceleration time (G) must be incorporated into the Acceleration Time (T) by multiplying the acceleration time on level ground (t) by the ratio of acceleration time (G).

10.3.2 Departure Time - Design Vehicle (TD)

The total time, in seconds, the design vehicle must travel to pass completely through the Clearance Distance (cd) is calculated using the following formula:

TD = J + T     equation 10.3a

where,

J = the perception-reaction time, in seconds, of the crossing user to look in both directions, shift gears, if necessary, and prepare to start (must use 2 seconds at minimum); and

T = the time, in seconds, for the grade crossing design vehicle to travel through the Vehicle Travel Distance (S) taking into account the actual road gradient at the grade crossing.

T may be obtained through direct measurement or calculated using the following formula:

T = (t x G)      equation 10.3b

where,

t = the time, in seconds, required for the design vehicle to accelerate through the Vehicle Travel Distance (S) on level ground established from Figure 10-2 Assumed Acceleration Curves; and

G = the ratio of acceleration time established from Table 10-1 Ratios of Acceleration Times on Grade or may be obtained through direct measurement.

10.3.3 Departure Time – Pedestrians, Cyclists and Persons Using Assistive Devices (TP)

The total time, in seconds, that pedestrians, cyclists and persons using assistive devices must travel to pass completely through the Clearance Distance (cd) is calculated using the following formula:

Tp=  cd / Vp      equation 10.3c

where,

cd = the Clearance Distance, in metres (Article 10.1); and

Vp = the average travel speed, in metres per second (m/s), for pedestrians, cyclists, and persons using assistive devices (to a maximum value of 1.22 m/s).

10.4 Gate Arm Clearance Time

10.4.1 Gate Arm Clearance Time is the greater of TG ssd or TG stop and represents the time, in seconds, it takes the design vehicle to travel from either the Stopping Sight Distance (SSD) position or the Stop position to the point past the gate arm.

Gate Arm Clearance Time from SSD postion (TG ssd) is calculated as follows:

TG ssd = cdG ssd/(0.27 x Vroad)    equation 10.3c

Where:

Vroad = the road crossing design speed over the crossing in kilometres per hour (km/h); and

cdG ssd = SSD + 2 m + L

where,

SSD is the stopping sight distance, in metres, and is calculated using the following formula:
SSD = 0.278 x 2.5 x V + d

  1. d = braking distance (m)
  2. V = initial speed (km/h)
  3. L = the total length, in metres, of the design vehicle

Gate Arm Clearance Time from the Stop position (TG stop) is calculated as follows:

TG stop = J + (t x G)

where,

J = 2 seconds, and is the perception-reaction time, in seconds, of the crossing user to look in both directions, shift gears, if necessary, and prepare to start; and

G = the ratio of acceleration time established from Table 10-1 Ratios of Acceleration Times on Grade or may be obtained through direct measurement; and

t = the time, in seconds, required for the design vehicle to accelerate through the Gate Arm Clearance Distance (cdG stop) on level ground established from Figure 10-2 Assumed Acceleration Curves;

where,

cdG stop = 2 m + L

where,

L = the total length, in metres, of the design vehicle.

Figure 10-2 Assumed Acceleration Curves

 

Text version of Figure 10-2

Source: Geometric Design Guide for Canadian Roads, published by the Transportation Association of Canada and dated September 1999

 

Table 10-1  Ratios of Acceleration Times on Grades

Design Vehicle Road Grade (%)
-4 -2 0 +2 +4
Passenger Car 0.7 0.9 1.0 1.1 1.3
Single Unit Truck & Buses 0.8 0.9 1.0 1.1 1.3
Tractor-Semitrailer 0.8 0.9 1.0 1.2 1.7

Source: Geometric Design Guide for Canadian Roads, published by the Transportation Association of Canada and dated September 1999

Table 10-2  Road Design Specification for Road Approach

SPECIFICATIONS
Column A Column B Column C
Rural Local Divided
Collector
Urban Arterial Not Divided
Expressway
Freeway

Table 10-3  Characteristics of Rural Roads

  Rural Locals Rural Collectors Rural Arterials Rural Freeways
Service function Traffic movement secondary consideration Traffic and land access of equal importance Traffic movement primary consideration Optimum mobility
Land service Land access primary consideration Traffic movement and land access of equal importance Land access secondary consideration No access
Traffic volume vehicles per day (typically) <1000 AADT <5000 AADT <1 2000 AADT >8000AADT
Flow characteristics Interrupted flow Interrupted flow Uninterrupted flow except at free flow (grade separated) major intersections
Design speed (km/h) 50 – 110 60 - 110 80 – 130 100 – 300
Average running speed (km/h) (free flow conditions) 50 – 90 50 – 90 60 – 100 70 -110
Vehicle type Predominantly passenger cars, light to medium trucks and occasional heavy trucks All types, up to 30% trucks in the 3 t to 5 t range All types, up to 20% trucks All types, up to 20% heavy trucks
Normal
connections
Locals
collectors
Locals
collectors
arterials
Collectors
arterials
freeways
Arterials
freeways

Source: Geometric Design Guide for Canadian Roads, published by the Transportation Association of Canada and dated September 1999

Table 10-4 Characteristics of Urban Roads

  Public Lanes

Residential
Public Lanes

Commercial
Locals

Residential
Locals

Indust./Comm.
Collectors

Residential
Collectors

Indust./Comm
Arterials

Minor
Arterials

Major
Expressways Freeways
Traffic service function Traffic movement not a consideration Traffic movement not a consideration Traffic movement secondary consideration Traffic movement secondary consideration Traffic movement and land access of equal importance Traffic movement and land access of equal importance Traffic movement major consideration Traffic movement primary consideration Traffic movement primary consideration Optimum mobility
Land service/ access Land access only function Land access only function Land access primary function Land access primary function Traffic movement and access of equal importance Traffic movement and access of equal importance Some access control Rigid access control No access no access
Traffic volume (veh/day) (typical)   <500   <1000   <1000   <3000   <8000   1000-12 000 5000 – 20 000 10 000 – 30 000 >10000 <20 000
Flow characteristics   Interrupted flow   Interrupted flow   Interrupted flow   Interrupted flow   Interrupted flow   Interrupted flow   Uninterrupted flow except at signals and crosswalks   Uninterrupted flow except at signals and crosswalks Uninterrupted flow except at signals Free-flow (grade separation)
Design speed (km/h) 30-40 30-40 30 – 50 30 – 50 50 - 80 50 - 80 40-60 50-90 80 – 110 80- 120
Average Running speeds (km/h)
(off-peak)
  20 - 30   20 - 30   20 - 40   20 - 40   30 - 70   30 - 70   40 - 60   50 -90   60 - 90   70 – 110
  Vehicle type Passenger and service vehicles All types Passenger and service vehicles All types Passenger and service vehicles All types All types All types up to 20% trucks All types up to 20% trucks All types up to 20% trucks
  Desirable connections Public lanes, locals Public lanes, locals Public lanes, locals, collectors Public lanes, locals, collectors Locals, collectors, arterials Locals, collectors, arterials Collectors, arterials, expressways, freeway Collectors, arterials, expressways, freeway Arterials, expressway, freeways Arterials, expressways, freeways
Transit service Public lanes, locals Public lanes, locals Public lanes, locals, collectors Public lanes, locals, collectors Locals, collectors, arterials Locals, collectors, arterials Express and local busses permitted Express and local busses permitted Express buses only Express buses only
Accommodation of cyclists No restriction or special facilities No restriction or special facilities No restriction or special facilities No restriction or special facilities No restriction or special facilities No restriction or special facilities Lanes widening or separate facilities desirable Lanes widening or separate facilities desirable prohibited prohibited
  Accommodation of pedestrians Pedestrian permitted, no special facilities Pedestrian permitted, no special facilities Sidewalks normally on one or both sides Sidewalks provided where required Sidewalks provided both sides Sidewalks provided where required Sidewalks may be provided, separation for traffic lanes preferred Sidewalks may be provided, separation for traffic lanes preferred Pedestrian Prohibited Pedestrian Prohibited
Parking (typically) Some restrictions Some restrictions No restrictions or restrictions one side only No restrictions or restrictions one side only Few restrictions other than peak hour Few restrictions other than peak hour Peak hour restriction Prohibited or peak hour restriction prohibited prohibited
Min. Intersection spacing1 (m) As needed As needed 60 60 60 60 200 400 800 1600 (between interchanges)
Right-of-way width (m) (typically)   6 - 10   6 - 10   15 - 22   15 - 22   20 - 24   20 - 24   202 - 453   202 - 453   >453   >603

Source: Geometric Design Guide for Canadian Roads, published by the Transportation Association of Canada and dated September 1999

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