Below are our top candidates for our design proposal to Kendal
- Chicanes
Chicanes are sections of the road’s shoulder that encroach on a lane, narrowing the road briefly (see figure 1&2). Narrowing the road has proven to reduce the speed of oncoming cars as they have to be more careful drivers, especially around object like chicanes. These sections often include greenery which could work to enhance the appeal of Kendal Dr, but this greenery would be somewhat limited because larger plants would require digging which is invasive. However, Kendal Dr is about 24 feet wide and narrowing the road further may pose a risk for emergency vehicles or semi-trucks, especially for cars or pedestrians that are present. For the chicanes to be effective, they would be about 3 feet wide into the road from each shoulder. This would reduce the size of the road to about 18 feet. Emergency vehicles like firetrucks are about 9 feet wide, leaving just enough room for them to maneuver without obstructing the other lane. If the chicanes were any smaller, they would not reduce speed as effective, and any larger would pose a major safety concern for emergency vehicles and anyone sharing that part of the road. Fixed objects like these chicanes also pose the risk of being struck, which may cause concern with the residents. The average speed reduction observed by these chicanes (per FHWA in the Virginia Department if Transportation’s Traffic Calming Guide for Neighborhood Streets) is 3-9 mph. The cost for a set of three is $10,000 for asphalt chicanes and about $16,000 for concrete.
| Chicanes | |
| Pros | Cons |
| Greenery improves aesthetic Speed reduction: 3-9 mph | Narrows road further (to 18ft wide) Lack of emergency/large vehicle accommodation Limited greenery based on size May be invasive depending on greenery Can be struck |
- Pavement Markings- Double Yellow Lines
Kendal Dr is a two-way road, so we would suggest adding a double yellow line. Double yellow lines are easily recognizable and do not physically restrict drivers, which means emergency vehicles and trucks are not hindered if they need to maneuver. From the VDOT Traffic Calming Guide, we know that a reduction of ½ mph is observed where shoulder markings narrow the travel-way, and a reduction of 2-3 mph is most commonly observed on streets where parallel parking is added to narrow the lane (pg.14). Since Kendal Dr does not have the space for shoulder markings or parallel parking, by restricting the driver to their half of the road, we believe the road to be narrow enough to have a similar speed reduction effect. Thus, we can estimate the lower bound of the speed reduction to be about ½ mph and the upper bound to be around 3 mph. The cost is estimated to be about $5 per foot, so with two lines and about 950ft of road, the total would be around $9,500 (pg.14). While this method may not have the most effective speed reduction, it is still a useful traffic safety control method and may even pair well with another calming method (see Speed Lump section below).
| Pavement Markings- Double yellow lines | |
| Pros | Cons |
| Easily recognizable Not obstructive Speed reduction: 0.5-3 mph Can be easily paired with other calming methods | Less effective for speed reduction on its own |
- Speed Table
A speed table are similar to the common speed humps except they are much wider and have a flatter “table”-like top area that offers a gentler transition. Not only would it be an annoyance for the residence to have to go over three abrupt speed humps to get home, but it would also force emergency vehicles to reduce their speed significantly which is unacceptable in the event of an emergency. The speed table offers a gentler transition so that emergency vehicles, buses, carts, shipping trucks, and residents, are less hindered. The average speed reduction for a 22ft wide speed table is about 6-9mph and about 4mph for longer tables. The cost per table is around $5,000-$15,000 depending on drainage and materials; though drainage should not be an issue as Kendal Dr. is slightly raised from ground level for most of its length, but we will look into this later in the project.
| Speed Table | |
| Pros | Cons |
| Accommodates all types of vehicles Gentler transition Speed reduction: 6-9 mph | Potentially more expensive |
- Speed Lump
A speed lump is a modified speed hump with gaps in it to allow emergency or large vehicles to pass through without needing to reduce speed. In the example in the figure above, the gaps are wide enough so that they do not allow for passenger vehicles to take advantage of them. However, the gaps in speed lumps can be tailored to accommodate any type of vehicle. In Arlington, Virginia, we have observed speed lumps that are made to accommodate police cars. In this case, passenger vehicles can cross into the middle of the road to take advantage of these gaps. We propose adding double yellow lines along with the speed lumps to deter this behavior. These gaps also mean less noise than speed humps from the larger vehicles. The average speed reduction for the speed lump is 5-7 mph. The cost for a speed lump is about $2,000, similar to the cost of a speed hump (depending on drainage and materials).
| Speed Lump | |
| Pros | Cons |
| Best accommodates emergency/large vehicles Can be adjusted to accommodate all types of vehicles Speed reduction: 5-7 mph Potentially least expensive | More abrupt than speed tables |
- Walking Path
Kendal Dr is commonly walked by the residents, but there is no path to walk on, forcing residents to have to share the road with vehicles. While it is not a traffic calming measure, we would like to suggest installing a walking path parallel to the road on the hill to the east of Kendal Dr. Originally, we considered paving a sidewalk, but it didn’t fit into our budget. We found that sidewalk concrete is on average $9 per square foot, so we estimated a 4ft wide concrete sidewalk stretching the length of Kendal Dr to be about $34,200, which would be $14,200 over budget (Weimert). Fortunately, after presenting an initial design review to Dr. Pegg, we learned that there is a separate budget allocated for installing sidewalks, so this does not need to be considered in the same budget anymore. However, a cheaper alternative to a sidewalk, a gravel path, may be a more cost-effective solution. We found pea gravel to be on average $50 per cubic yard, so we estimated a 4ft wide 2in deep gravel path that extends the length of the road to be about $1,200 for the pea gravel and $8,000 for the gravel grid to set it in (see figure 13 above), coming to about $9,200 (Carter). This gravel path is significantly cheaper than the sidewalk, which allows more money to be allocated to traffic calming measures or adding more walkways around the neighborhood to further increase the safety and convenience of the residents.
| Adding Walking Paths | |
| Pros | Cons |
| Budget is separate from the traffic calming methods Residents no longer have to share the road Improves safety and convenience for residents | Sidewalks can be expensive Difficult to add adjacent to the road due to the slope on each side |
Below is our plan for the layout of traffic calmers. The VDOT traffic calming best practices document we’ve been consulting suggests an optimal calmer frequency of 150-300 feet. We’ve put them 245ft from each other, starting at a part of the road that is particularly unsafe for pedestrians: the point where the footpath meets that road. We expect a concentration of pedestrian activity in this area, so a calmer right next to it should make it much safer. In addition, it is only 75 feet from the stop sign, so the expectation is that vehicles will be discouraged from accelerating at a dangerous level.
