Gestión de riesgos financieros 1. Riesgo operacional

Basic Principles

Discontinuous bus lanes are developed on the basis of the following principles: • To minimise external interferences for buses on non-signal affected segments, • To reduce obstructions of buses due to long or severe queues21 at traffic signals,

• To increase the number of buses that can be released during one cycle length at traffic signals,

• To provide an adequate level of traffic flow quality for buses at signalised intersections, • To reduce negative effects of bus lanes on capacities of intersection approaches, and • To reduce negative effects of bus lanes on traffic flow quality of other vehicles.

Arrangement

Basically, a discontinuous bus lane is allocated on the rightmost lane of a direction as presented in Figure 50. This lane is formed by the distances from its first end to the stop line, denoted l1,

and from its second end to the beginning of the downstream intersection, denoted l2.

The distance l1 can be calculated if an intended value of degree of saturation is assigned to the

bus lane (more details are provided in Appendix A, part A.5). On the one hand, this value should not be too high in order to give precedence to buses over other vehicles; on the other hand, it should not be too low since traffic flow quality of other vehicles might be impacted severely. Thereby, the selection of this value should be consistent with the predefined principles. When traffic-dependent control strategies are applied, different degrees of saturation can be resulted for the bus lane at traffic signals. In that case, the influence of those control strategies should be covered when selecting this distance.

1 l Signal for vehicular traffic

Pedestrian signal

Loop detector (DK) for monitoring congestion Legends:

2 l

DK1 DK2

Auxiliary signal (yellow flashing light)

BU

S

LA

N

E

Figure 50: An arrangement of discontinuous bus lane

The distance l2 is determined so that the narrowing roadway part in the downstream intersection

due to the arranged bus lane will not have considerable impacts on capacity and traffic flow quality of the upstream approach. The recommended value for l2 is given as follows:

   = u l m l2 max 90 (5-1) where lu = 3⋅tG (5-2)22 lu = length of unchanged number of lanes on the downstream subsection [m] tG = green time of the upstream approach [s]

If the entry of the bus lane is potentially blocked by queuing vehicles, the use of congestion detectors DK1, DK2 (see Fig. 50) and traffic-responsive control is recommended to monitor the limitation of occurring queues. Depending on certain conditions, these detectors should be placed at relevant positions in order to eliminate a blockage of the bus lane.

Operational Principles

After being discharged from the preceding intersection, buses will join their lane at a certain point on the downstream section (see Fig. 50). On this roadway part, a separate lane is provided for the exclusive use of buses. Thereafter, they will rejoin the mixed traffic lane at another point near the traffic signals. The roadway part ahead of the bus lane is allocated for both buses and other vehicles.

Auxiliary signals (yellow flashing light), relevant traffic signs, and pavement markings must be provided to notify other road users of the discontinuous bus lane being disposed ahead. Consequently, other vehicles on the rightmost lane will divert to adjacent lanes as soon as the information of the forthcoming bus lane is ascertained.

If the bus lane is potentially blocked by extensive rear queues, the use of traffic-responsive control with relevant control strategies (e.g. green time adjustment) must be implemented. In that case, the length of queues on adjacent lanes is monitored by inductive loops (DK1, DK2). As a result, a free entry of buses to their discontinuous lane can be guaranteed.

Recommendations on Application

In order to arrange discontinuous bus lanes, the direction must contain at least two travel lanes. In addition, the length of road sections between consecutive intersections must be long enough to realise these lanes. The minimum value of 3·l2 is recommended for this length. These

requirements are considered as prerequisite conditions for an application of this measure.

Generally, this measure could be preferable to directions that operate with a relatively high bus volume (e.g. greater than 20 buses/h) and a low proportion of right-turning traffic (e.g. less than 10%) at the forthcoming traffic signals. When right-turning traffic is noticeable, in particular with its large number of four-wheel vehicles, capacity of intersection approaches can be affected considerably due to impediments of skewing movements. Besides, left-turning buses should not be allocated to operate on these lanes since they can cause impediments for other vehicles due to their skewing movements at traffic signals.

Moreover, this measure is preferably implemented at isolated intersections because of the predefined objectives regarding the utilisation of capacity. For this reason, the areas ahead of bus lanes can be used by both buses and other vehicles in queue or motion.

Traffic control is an important factor for this measure. Traffic engineering installations such as auxiliary signals, traffic signs, guidance panels, strips for bus lane separation, and pavement markings must be implemented properly. Additionally, parking activities and other potential disturbances should be completely restricted on the segments involved. Crossing and accessing

traffic from side streets or alleys should be regulated carefully by right-of-way rules or signalisation. Besides, traffic enforcement should be conducted strictly.