Breaking News

Precipitation intensity for highway & bridge drainage design

Bridge with mist

Drainage projects usually consider a precipitation intensity based on the time of concentration and the return period. However, when designing drainage systems for bridges and highways it is important to verify the compatibility between the precipitation intensity and the driver's safety. Thus, two additional criterion should be considered: Hydroplaning and visibility.

Hydroplaning
Hydroplaning is the situation when when a layer of water is built between the wheels of a vehicle and the road surface.

Hydroplaning leads to a loss of traction. The driver  of the vehicle looses control and the vehicle begins to slide. The hydroplaning of a vehicle is a function of the speed, the water depth and the inflation pressure of the wheels.

car security and car accidents due to rain
Figure 1. Hydroplaning concept (Source: Tirebuyer)

The hydroplaning based intensity is a new approach to drainage design. It seeks that rainfall that is just sufficient to cause a water depth of sheet flow at the edge of the traveled way that will cause hydroplaning.

The design concept is that removal and control of flooding, caused by rainfall in excess of rainfall that will cause hydroplaning, is overdesign from a vehicle safety standpoint.

The limit speed is defined by the standards of the highways or bridge deck. Then, the speed that initiates hydroplaning is used for defining the water depth D when hydroplaning occurs. The most popular studies about hydroplaning speed are the studies performed by NASA and Gallaway et al., (1979). Then, it is assumed that water flows in sheet with depth D across the surface to the edge of the gutter.

Combining the depth D with the rational formula and the Manning equation it is possible to define the hydroplaning design rainfall intensity.

Hydroplaning and vehicle speed
Figure 2. Hydroplaning speed equation reported by Gallawat et al., (1979).

Visibility
The rainfall and the windshield wipers reduce the visibility of the driver. Such visibility reduction also reduces the safe stopping distance.

driving car in rain
Figure 3. Driver visibility during rain (Source: Earth magazine)

The visibility design concept is that drainage removal or control of flooding caused by rain in excess of that rain, which will cause driver vision impairment, is overdesign from a vehicle safety standpoint (more drainage capacity than required).

The safe stopping distance is a function of the vehicle speed and the mechanical characteristics of the vehicle (break time and deceleration). Thus, this design criterion uses the rain intensity that allows a visibility equal to the safe stopping distance.

Several studies analyzed the visibility considering the effect of different rain intensities and windshield wipers. One of the first methods for estimating the driver's visibility under different rainfall intensities and vehicle speeds is based on the experiments from Ivey et al., (1975).

We can see that there is no single method for estimating the rainfall intensity. Thus, the selection of the highway-bridge rainfall intensity is a multi-criteria process. It is suggested to consider all the criterion; the two criterion from this post and the traditional IDF - rational criterion. Then, engineering criterion should decide the optimum one.

If you require advice for design of highway/bridge drainage or doubts about the rainfall intensity, feel free to contact us.

civil engineering design
Figure 4. Driver visibility suggested by Ivey et al., (1975)

5 comments

Daniel Bryan said...

Very Interested site this is. I truly Enjoy a lot reading your Blog. I will Bookmark your site for more reference. this is very nice post. it is very helpful for us.
Thanks...
External drainage

Vadyman said...

Glad you like it. If there is topic you would like to suggest, fell free to do it

elvina roy said...

After reading this amazing and informative post this was very amazing discount code and delivery much better experience visit at the uber promo code 50

Maria Adam said...

Looking for a way to save on shipping costs while shopping for designer brands? Look no further than Hautelook Discount Codes Free Shipping! With our extensive collection of products, you're sure to find what you need. Claim your discount now and upgrade your style!

Jennifer Walsh said...

I found your blog post on precipitation intensity for highway and bridge drainage design very informative. It's crucial to consider the intensity of rainfall when designing drainage systems for infrastructure projects. By the way, if you're interested in outdoor equipment and gear, you can find great deals and discounts at "https://couponsjournal.com/scheels-coupons". Keep up the excellent work!