Design Standards for Junction Improvements - Report Example

Junction design Junction design Development scenario and possible challenges It is important to that while multiple scenarios existed with regard to remodeling of the junction, the proposed plan is focused on one that will provide maximum benefits and return to the users and the public in general. This calls for multiple considerations. Three most viable scenarios are described in the table below: Scenario 1: Minimal work (low cost) Leaving the existing network intact without making any modifications save for resurfacing immediate points of connection to the introduced connection route. Scenario 2: moderate accompanying refurbishments (low cost) Modifying the immediate major feeder roads to match the expectations of the ideal design for the junction. Scenario 2: Extensive work (high cost) Modifying all the minor and major feeder roads as well as the immediate link areas to major roads to be fed by the junction. Just as the level of work dictates, the three scenarios are more capital intensive as the work increase. However, with more work employed, so is the nearness towards creation of an ideal connection route and hence more effective in meeting public needs. Extensive work is also expected to create additional disturbances and challenges and hence there is a need to create a balance. The main environmental aspects considered in this report include: geology and soils, surface and groundwater conditions, air quality issues, generated noise, flora and fauna, landscaping and visual impact, cultural heritage, as well the population and general economy (OFlaherty, 2002, p. 123). This basically involves identification of the environmentally sensitive aspect along the connection route. It should be noted that no biodiversity areas under national or international legislation protection have been identified as lying along the area of construction. However, usage of natural resources including water resources, agriculturally viable land as well as forests is reviewed in the report. Improvements proposed Design standards for Junction Improvements. Design elements: Channelization: The movement of traffic flow at intersections to specified lanes and paths, by way of traffic marks is referred to as channelization. Channelization works for segregation of conflicts, regulation of conflict angles, regulation of speed, securing of automotive leaving or crossing the major traffic streams, securing of pedestrians, getting rid of excessive intersectional areas, blocking of prohibited movements as well as positioning of traffic regulation devices (Silver & Corbin, 2008). Design speed: The design speed at the intersection will help in governing multiple elements including entry – exit radius as well as the inscribed diameter. The design speed at the intersections in this case will vary from 20kmph to 25 kmph. Radius at entry: The radius at entry is defined by the design speed adopted, super elevation as well as the coefficient of friction. The radius should amount to drivers reducing their speeds to the design speed limit of the rotary. A range lying between 15 and 25 m is considered appropriate for the junction in question. Radius at exit: The exit radii should exceed the entry radii in order to enable the vehicles to increase speed while getting off the intersection. A range lying between 20 and 35 m is to be adopted in the remodeled design. A reduced radius may be chosen if the design speed at the point of exit calls for low speed due to high pedestrian flows as well as the site conditions. Width of carriageway at entry and exit: The carriageway width with regard to the intersection legs is regulated by the design year traffic getting into and leaving the junction. The width at point of entry and point of exit depends on the carriageway width of the approaching road. The carriageway width with respect to the approaching road is dependent on the number of lanes that needs to be accommodated in each and every direction which largely depends on the volume of traffic entering and leaving the junction. The width of the point of exit needs to always exceed or be equal to the width at point of entry in order to facilitate free movement of the incoming traffic towards the junction. The increments in delays which will be witnessed at some locations with the connection route introduction are insignificant, and will be exceed off-set resulting from lowered speeding, a traffic calmed environ as well as raised safety and aesthetic considerations. For various movements, resulting delays would literally slightly reduce given that through traffic will not be delayed by left-turning motorists (Silver & Corbin, 2008). It is also important to emphasize that the left-turn lanes are recommended as being appropriate for locations where there are increasingly significant left-turn volumes either regularly or at specific peak durations such as schools, markets, or busy shopping malls. No reduction in lanes is recommended for any of the feeder roads given that this would raise delays. Places with reduced left-turn movements which do not require a distinct left-turn lane, will be provided with a break in the median and hence allow left turns easily. History of crashes and accidents in general in the region of the roads construction is an important element in its feasibility study as well as a means of coming up with appropriate measures to curb the same in future. Previous figures indicate that over the last four years the stretch extending along junction experienced a total of twelve injury resulting crashes as well as 67 property damage-only crashes. Majority of the crashes were recorded at the intersections, basically at the intersection of the ways which experienced an average of 24 crashes annually. Additionally, the accident reports indicated that 19% of the accidents were fixed-object crashes whereby vehicles either hit a nearby pole, a nearby tree or walls located at the side of the road. Additionally, overtaking as well as right-turn and left-turn collisions of 2 vehicles moving side-by-side along incoming and roads section comprised of16% of accidents recorded along the road. Of interest also was the fact that the feasibility evaluation, based on exiting data concluded that a percentage exceeding 35 of accidents are as a result of high speeding by motorists. Introducing reasonable spaced controls was therefore identified as a possible means of alleviating the problem of over-speeding and hence the number of accidents to be recorded in the new construction. This will also lower the severity of accidents recorded if any. Another interesting factor was the realization that 56% of the accidents relating to fixed-object collisions in the roads within the area took place during the night. This was mainly attributed to the headlight glare and hence a raised median with necessary landscaping was identified as a possible means of reduce the amount as well as the severity of collisions in the area. Successful design is pegged on the ability to not only come up with appropriate design but also develop a road that meets the transport requirements of the region within which the junction will serve (Kostof, 2007, P. 34). This is pegged on proper understanding as well sufficient background knowledge of the traffic associated with feeder roads that will serve the road with traffic. The existing and the remodeled situations are illustrated below: Traffic signal regulations are mainly implemented as a way of reducing or completely eliminating conflicts possible to occur at the intersections. They accomplish this through allocation of green times among the multiple users at the intersections. Signal regulations differ from non-sophisticated methods, which establish the timing settings on specific times into complex algorithms that in turn calculate the green time appropriation in real time on basis of the traffic volumes (Rodger, 2002). According to the TCS Handbook model for actuated control in estimation of the cycle length, this is a very important parameter in determining efficiency. For instance, given the demands on Lane sections 1, 2, 3, and 4 as 488 vph, 1317 vph, 488 vph, and 878 vph respectively, the estimated green durations for two phase groups of through movements need to be optimal green times while the cycle length needs to be close to the optimal cycle duration. If we make use of TSC Handbook model, the estimated cycle length is merely 104 seconds. At this demand level, the capacity of lane sections 1, 2, 3 and 4 given as; …..1 It is important to point out that all the lane groups have adequate capacities for flow of junction. It should be noted that traffic arrivals are random. It is also important to note that some cycles may not be successful in serving the queues on various lane groups with a high v/c ratio such as one with a flow ratio being 0.98. This will amount in a lengthier delay on lane sections 4 and 8. Additionally, shorter cycle length also raises total lost duration during a given cycle. As a result, the level of demand, the traffic controller operates with optimal greens for phases 2, 6, 4, and 4. It is important to mention that the design takes into consideration multiple factors that impact on road construction projects. Other than considering the environment within which the road is to be constructed, the design takes into consideration legal guidelines and requirements affecting road constriction within the region of interest. Additionally, it details three possible scenarios that may be undertaken in the road construction project. The report also details various parameters and variables of interest during the projects implementation phase. On the approaching the red signal, a green signal will be required upon the arrival of a vehicle on the approach. This demand is stored within the controller that then serves the stages in cyclic order omitting any of the stages in which no demand has been registered. Where it is necessary that one stage need to always follow another, the first stage’s appearance will automatically put in place a demand for the second stage. When one stage loses right of way on an optimal green period alteration, a demand is put in place for a reversion to the stage after other demands are successfully accomplished. When a green signal is shown, the duration for which it is shown may be extended by motor vehicles detected moving towards the traffic signal. The reason for this extension, or the summation of various extensions, is to allow vehicles to go through the stop line prior to the optimal green period being reached. The loss is obtained as follows, for a parked car approaching causing an effective width loss, which is expressed as shown below: Whereby z (>7.62) shows the distance from the stop line of the given parked car while g is the green time in seconds. Traffic signal calculations are as shown in the table below: References Kostof, S. (2007), The City Shaped: Urban Patterns and Meanings Through History. London: Thames and Hudson Ltd. OFlaherty, O. (2002), Highways the location, design, construction and maintenance of road pavements. Oxford: Butterworth-Heinemann. Rogers, M. (2002), Highway engineering. Oxford, UK: Blackwell Science. Silver, C. & Corbin, M. (2008), Planning the Twentieth-Century American City. Johns Hopkins University Press. Read More