Roundabout Research
Posted: August 27th, 2021
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Roundabout Research
A roundabout refers to a circular intersection that enables counter-clockwise traffic movement. Usually, it is built around a central island, which implies that vehicles entering the surrounding road are subject to circular movement (CSU Construction Standards). A roundabout is usually characterized by various features that include a circulatory roadway, splitter islands, and central islands. Further, when constructing a roundabout, two main principles should be considered to ensure its effective operation. These include the first utilization of a geometric design to help achieve speed reduction at the entry and through the intersection (CSU Construction Standards). Secondly, the yield-at-entry rule that demands that traffic entering yields to traffic traveling in the circulatory roadway. Thus, adequately constructed roundabouts will reduce conflict points resulting from collisions, reduced vehicular speeds, and enhance the continuous flow of vehicles, among other benefits. Therefore, the study seeks to design a roundabout at the intersections of New Meridian and Pitkin that will accommodate bicycle and pedestrian movement. The newly designed intersection should account for the Stadium, the future Meridian Village residence hall, the city of Fort Collins Pitkin Bikeway, and the Transfort buses’ movement through the intersection. According to a cordon study, the roundabout is estimated to contain about 200 cyclists in peak hours. Hence, this paper aims to discuss the appropriate location of the roundabout design, possible alternatives for the design, benefits to pedestrians and bicycles, and associated cost estimates.
Best Design Fit for the Roundabout
The best design for a roundabout that caters to this kind of intersection is the multilane roundabout that can accommodate a desirable maximum entry speed of 20 to 30 meters per hour. This design will have at least two maximum number of entering lanes for every approach with a typical inscribed circle diameter of 150 feet to 300 feet on a raised central island. The following figure illustrates a typical multilane roundabout that would be adopted in this design;
Figure 1: design of a typical Multilane roundabout
The intersection will be designed with entries from 2 approaches that flares to over two lanes. Therefore, this is meant to ensure easy vehicular movement to allow pedestrians and bicycles free movement across the roundabout.
Location of the Roundabout
The roundabout will be located at the intersections of New Meridian and Pitkin, characterized by closely spaced intersections; hence it is not possible to achieve signal progression. It is meant to accommodate bicycle and pedestrian movement by catering for the Stadium, the future Meridian Village residence hall, the City of Fort Collins Pitkin Bikeway, and the Transfort buses’ movement through the intersection. Figure 2 below shows the location of the intersection (adopted from Google Maps).
Figure 2: Intersections of New Meridian and Pitkin
The engineering team will deliver CAD drawings of the roundabout and adjacent sidewalks, water retention/stormwater, transit turning radii, and aerials. The team will also provide a cost estimate for the project that accounts for a concrete road surface. Thus, an engineering firm’s renderings will be shared with the project team to help develop conceptual options.
Benefits for Pedestrians and Bike Traffic
The New Meridian-Pitkin intersection roundabout will be designed with a greater focus on pedestrians’ safety of all ages and abilities. Hence, it will concentrate on lowering vehicle speeds and short crossing distances, which will enhance pedestrian movement. Further, this intersection will be provided with high visibility such that drivers have clear visuals when entering and exiting the roundabouts (CSU Construction Standards). Simultaneously, the design will include supporting visibility using intersection lighting to reduce silhouetting at the crosswalks. Equally, the pavements will be provided with adequate and appropriate markings and signs (CSU Construction Standards). Hence, this will enable recognition of pedestrian passages, allowing them sufficient time to move around the roundabout.
Second Alternative Design Fit for Roundabout
The second alternative design fit for the roundabout is the single-lane design. The design features a single-lane entry at all the legs. It is provided with one circulatory lane, as illustrated in figure 3 below.
Figure 3: Single-late roundabout design
Hence, the single-lane roundabout differs from the mini-roundabout because they are inscribed with large circle diameters and a non-traversable central island, truck apron, and crosswalks (page. 4-source 2). The design allows relatively high speeds along circulatory roadways, at the entry and exit points.
Benefits for Pedestrians and Bike Traffic
Moreover, this type of roundabout has several benefits for pedestrians and bike traffic. Since it provides one direction flow of pedestrians and bike traffic, it helps reduce their conflict locations with the vehicles (Larimer County/ City of Fort Collins / City of Loveland 1075; CDOT Roundabout Design, 5). At the same time, motorist speed is effectively reduced, thus enabling a good flow of both traffics.
Third Alternative Design Fit for Roundabout
The third best alternative is the mini-roundabout. This design is a small single-lane intersection consisting of a complete traversable central island. It is commonly constructed in low-speed urban environments with an average operating speed of about 30 miles per hour or less (CDOT Roundabout Design, 3). Given that there is a high traffic flow for pedestrians and cyclists, the New Meridian and Pitkin intersection, this speed level will be appropriate to help reduce the motorists versus pedestrians and cyclists traffic, which often contributions to fatal collisions. Figure 4 below illustrates the design.
Figure 4:
Mini-Roundabout Design
The intersection is characterized by limited right-of-way that could hinder free vehicular movements. Hence, the mini-roundabout is the most appropriate since it will provide a completely traversable central island that can easily accommodate large vehicles. It can also effectively accommodate passenger cars (CDOT Roundabout Design, 2). Therefore, this design is beneficial to pedestrians and bike traffic since they provide short crossing and enhance low vehicle speeds both in the entry and exits.
Cost Estimates for the Roundabout Designs
The following table provides a cost estimate of each of the proposed roundabout designs. The estimates are based on the current market price estimations.
Table 1: Cost Estimate for the proposed Designs
| Mini-Roundabout Design | Single Roundabout Design | Multi-Roundabout Design | |
| Item Description | Amount/Cost | Amount/Cost | Amount/Cost |
| General | $ 60,000.00 | $ 72,000.00 | $ 90,000.00 |
| Site Preparation | $ 38,000.00 | $ 45,600.00 | $ 57,000.00 |
| Earth works | $ 480,000.00 | $ 576,000.00 | $ 720,000.00 |
| Drainage | $ 580,000.00 | $ 696,000.00 | $ 870,000.00 |
| Roadworks | $ 790,000.00 | $ 948,000.00 | $ 1,185,000.00 |
| Concrete footpaths, cycle ways, layback and driveways | $ 380,000.00 | $ 456,000.00 | $ 570,000.00 |
| Service Utilities | $ 290,000.00 | $ 348,000.00 | $ 435,000.00 |
| Landscaping | $ 80,000.00 | $ 96,000.00 | $ 120,000.00 |
| Total Cost | $ 2,698,000.00 | $ 3,237,600.00 | $ 4,047,000.00 |
Table 1 shows the cost estimates
for the three roundabout designs. The mini-roundabout design has the lowest
cost, estimated at US $
2,698,000, followed by single roundabout design with US $ 3,237,600. The multilane roundabout is the most expensive with about Us $ 4,047,000. This is because it is more detailed in the planning and requires large space, hence high investments to ensure its completion.
Works Cited
CDOT Roundabout Design, Chapter 19. Accessed 25th October 2020 fromhttps://www.codot.gov/business/designsupport/bulletins_manuals/cdot-roadway-design-guide-2018/dg18-ch19
CSU Construction Standards. Accessed 25th October 2020 from https://www.fm.colostate.edu/constr_standards
Larimer County/ City of the Fort Collins / City of Loveland; Urban Area Street Standards. Accessed 25th October 2020 from https://www.larimer.org/sites/default/files/uploads/2017/lcuass_2016.pdf
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