“Architects and engineers are few lucky people for they build their monuments on public consent, on public approval and often using public money.”

AbstractIn the Year 2000 The Total Population of Thimphu was

43,479

98,676 in the year of 2005

This means the population got increased by 2.27 times in five years

According to the ‘Thimphu Structure Plan 2002 to 2027’ the city is expected to have 3.73 times the population size of what it had in year 2000, which means Thimphu will have to shelter 162,327 people.

Thimphu will face many difficulties which would require engineering solutions.

Doebum Lam which origins from Memorial Chortenand ends connecting Chhubha Chhu Circle with Memorial Chorten is also called Royal Boulevard.

Ever since Norzin Lam was made one-directional lane, Doebum Lam as per TSP is suppose to handle the traffic pressure.

4-lane carriage way with 0.75m wide separator in the centre, dividing each 2-lane carriage ways in different directions.

Total of 4.5 square meters of parking space is provided along the Royal Boulevard.

The length of Doebum Lam is 1.6km

Doebum Lam at Swimming Pool Junction provides vehicles to change lanes without proper designed rotary

Hence this region is more accident prone for both vehicles and pedestrians who cross these lanes

In spite of two built up Subways (Underpasses), the pedestrians prefer not to use them due to lack of proper maintenance. This just leads to functional failure of those two underpasses.

Design of RotaryDefinitions:

At-grade intersection: an intersection is where all roadways join or cross at the same level.

Diverging: the dividing of a single stream of traffic into separate streams. Intersection Angle: the angle between two intersection legs. Merging: the converging of separate streams of traffic into a single stream. Rotary Intersection: a road junction laid out for movement of traffic in one

direction round a central island. Rotary Island: a traffic island located in the centre of an intersection to compel

movement in a clock-wise direction and thus substitute weaving of traffic around the island instead of direct crossing of vehicle pathways.

Weaving: the combined movement of merging and diverging of traffic streams moving in the same general direction.

Weaving Length: the length of a section of a rotary in which weaving occurs.

Advantages of Rotary Intersections

An orderly and regimented traffic flow is provided. Individual traffic movements are subordinated in favor of traffic as a whole.

All traffic proceeds at a fairly uniform speed. Frequent stopping and starting are avoided.

Weaving replaces the usual crossing movements at typical at-grade intersection. Direct conflict is eliminated, all traffic streams merging or diverting at small angles. Accident occurring from such movement are usually of a minor nature

Rotaries are epically suited for intersections with five or more intersection legs though these can also be adopted at intersections with 3 or 4 legs.

For moderate traffic, rotaries are self-governing and need no control by police or traffic signals.

Disadvantages of rotary Intersections

Once the rotary has locked up the movement of vehicles completely stops and the traffic will have to be ultimately sorted out by the police.

A rotary requires a comparatively larger area and may not be feasible in many built up locations.

Where pedestrian traffic is large, a rotary by itself is not sufficient to control traffic and has to be supplemented by traffic police.

Where the angle of intersection between two road is too acute, it becomes difficult to provide adequate weaving length.

The provision of rotaries at close interval makes travel troublesome.

Traffic turning right has to travel a little extra distance.

Width of weaving SectionThe width of the weaving section of the rotary should be one

traffic lane (3.5m) wider than the mean entry width thereto.

Capacity of the RotaryCapacity of the individual weaving sections depends on

factors such as (i) width of the weaving section (ii) average width of entry into the rotary (iii) the weaving length and (iv) proportion of weaving traffic and

The Capacity of the Rotary will be calculated

Qp= Practical capacity of the weaving section of the rotary in passenger car units (Pcu) per hour.

w= width of weaving section in metres (within the range of 6-18 m)e=average entry width in metres (i.e., average of ‘e1’ and ‘e2’), e/w to

be within a range of 0.4 to 1.00l= length in metres of the weaving section between the ends of

channelizing islands (w/l to be within the range 0.12 and 0.4)p=proportion of weaving traffic, i.e., ratio of sum of crossing

streams to the total traffic on the weaving section (p=(b+c)/(a+b+c+d)), range of being 0.4 to 1.0

Total hourly Traffic Volume

Total Hourly Traffic Volume = 1796 per hr.

Calculation of traffic proportion:

P1=0.71P2=0.839P3=0.813P4=0.737

Design of Rotary with Standard Weaving Length

Weaving length=40mWidth of carriage at entry(e1)=6.5mWidth of carriage at exit=6.5mWidth of non-weaving section(e2)=6.5mWidth of weaving section(w)=10mCapacity Qp =2661 passenger car units (Pcu) per hour

Design of rotary wit widened road but with manipulated weaving length

Radius of central island=3.5mWeaving length=12.5125mWidth of carriage at entry(e1)=6mWidth of carriage at exit=6mWidth of non-weaving section(e2)=6.5mWidth of weaving section(w)=9.75m Capacity Qp = 1832 passenger car units (Pcu) per hour

Desing of rotary without road widening

Radius of central island=3mWeaving length=12.35mWidth of carriage at entry(e1)=4.4mWidth of carriage at exit=4.4mWidth of non-weaving section(e2)=6.4mWidth of weaving section(w)=8.425m Capacity Qp=1660 passenger car units (Pcu) per hour

Pedestrian Overpass and UnderpassPedestrian overpasses and underpasses allow for the uninterrupted flow of pedestrian movement separate from the vehicle traffic.However, they should be a measure of last resort, and it is usually more appropriate to install safe crossings that are accessible to all pedestrians.Studies have shown that many pedestrians will not use an overpass or underpass if they can cross at street level in about the same amount of time or less.

PurposeProvide complete separation of pedestrians from motor vehicle trafficProvide crossings where no other pedestrian facility is availableConnect off-road trails and paths across major barriers

ConsiderationsUse sparingly and as a measure of last resort. Most appropriate over busy, high-speed highways, railroad tracks, or natural barriers.Pedestrians will not use if a more direct route is available or if the grade is relatively flat.Lighting, drainage, graffiti removal, and security are also major concerns with underpasses.Must be wheelchair accessible, which generally results in long ramps on either end of the overpass.

Underpasses for Doebum Lam

Present subways

Currently there are two underpasses for Doebum Lam. One is located near the Swimming Pool Junction and the other one is located near the Chhubha ChhuCircle below Changangkha School. The current situations of these two underpasses are:1. The underpasses are not used by the pedestrians2. The underpasses are not in condition to be used3. The underpasses are facing water leakage problem from the adjacent drains

present, making the subways slippery and not usable for the general public4. The underpasses don’t have proper lighting facilities5. The underpasses are used as toilets by the general publicWith all the points keeping in mind, one can conclude that the subways are facing functional failure.

Reasons for functional failure of these two Underpasses

The pedestrians prefer to cross the road from the part where the separator blocks are removed. This causes inconvenience for both pedestrians as well as vehicles and both the parties are prone to inter or intra accidents. Underpasses situated below the road, seeing at those just gives the pedestrians a notion, that it is tiresome job to go through them.The subway is not in a condition to be used.No proper lighting facilities are provided for these subways, so, it just is inconvenient to be used at nights.

Comment: The problem for both the vehicles and pedestrians is that, the peak hours for both of them coincides and level of service is not enjoyed by both of them.

Proposals for the Underpasses to attract Pedestrians

Keeping the subway clean and providing it with lighting facilities.The walls too need to be renovated and just like any other underpasses; this underpass too deserves decoration which would be source of attraction for general public to use the pedestrians. The walls either should be tiled or plastered in order to look usable. The floor too needs to be renovated with tiles or marble or any other flooring material that gives the subway an expensive look. Proper accessibility should be provided especially for the one situated at the Swimming Pool Junction.

Thank You