S2_volume-counts-and-concepts-traffic-engineering (1).pdf

TRANSPORTATION ENGINEERING Explanatory Session: «Volume Counts and Concepts of Traffic Engineering»

CONTENIDOS Volume Counts

Concepts of Traffic Engineering

Exercises

Supply and Demand in Transportation

Supply and Demand • Review the reading material and answer the question:

What represents the supply and demand in Transportation Engineering?

Volume Counts

Determing the Demand - Traffic Volume Counts • When we talk about the supply and the demand. The question is, how can we determine what (is/will be) the demand in a highway? • What is the current demand?, • What will be future demand? For an existing roadway. • What types of projects would be required for the future demand?

Vehicle Count Methods • In-Situ Conventional Technologies • In-situ refers to measured traffic data with placed detectors next to the roadway • Two types • Intrusive (data registration and a sensor) • Non-Intrusive • Intrusive Methods • Pneumatic Tubes • Piezoelectric sensors • Magnetic circuits

Vehicle Count Methods • Pneumatic Tubes

They register the pressure changes when a vehicles passes by the tube Disadvantages:  Volume per lane, no turns  Limited by climate and traffic (multiaxis)  Problems with slow traffic or congestion

Vehicle Count Methods • Piezoelectric Sensors

 Different from the pneumatic tube, the sensor is capable of

registering speeds and weights  It is useful for the WIM (weight-in-motion) stations

• Magnetic circuits: used in Europe but short-lived and affected by heavy traffic

Vehicle Count Methods • In-Situ Conventional Technologies • Non-Intrusive Methods • • • • • •

Manual counts Passive and active infrared Passive magnetic Microwave radar Passive ultrasonic and acoustic Video detection

Vehicle Count Methods • Manual counts • Most used traditional method • Experienced measurers • Besides volume data, the measurers can also get valuable information that is hard to acquire automatically like • Vehicle occupational rate • Pedestrians • Vehicles types • Tools used: • Counting sheets • Mechanical counting tables • Automatic counting tables

Vehicle Count Methods • Passive and active infrared • Counts, speed and type can be measured • However, there are limitations due to crossing vehicles, and adverse climate

• Passive Magnetic • Problems with congested areas

• Microwave radar • Similar to infrared • Mainly used for traffic infraction detection

Vehicle Count Methods • Passive Ultrasonic and Acoustic • Affected by climate conditions • Video Detection • Number of vehicles • Type of vehicles • Speed • Occupational Rate • Pedestrians • The post-processing is long and constant

Video Detection

https://www.youtube.com/watch?v=z1Cvn3_4yGo

https://www.youtube.com/watch?v=ufK2XRGUjuc

Manual Counts • It consists in summarizing in a predetermined format what is observed in the field.

• The format sheets have information like: • Vehicle types • Time intervals (15 min) • Intersection turning type and street

Hourly Partition – 15 mins

Type of Vehicles

Then, the several tables are put together

Traffic Volume Count Programs

http://www2.dot.state.fl.us/FloridaTrafficOnline/viewer.html

Concepts of Traffic Engineering

Traffic Parameters • AADT = Annual Average Daily Traffic It represents the arithmetic average of the daily volume counts in one year, existing or predicted for a given section. Knowing AADT gives the engineer a quantitative idea of the importance of the section and allows to make economic feasibility calculations. In Spanish, it is called IMDA = Indice Medio Diario Anual • How AADT is calculated?

Traffic Parameters • AADT = Average of 365 ADT (Average Daily Traffic)

ADT  AADT  365

 For a specific day can be calculated by:  Counts = field measurement  HF = hourly factor  DF = daily factor  MF = monthly factor  GF = growth factor

 1  ADT  counts  DF MF GF   HF 

Traffic Parameters • Annual average daily traffic (AADT) – Annual traffic averaged on a daily basis – Both directions

• Design hourly volume (DHV) – Traffic volume used for design calculations

– Typically between the 10th and 50th highest volume hour of the year (30th highest is most common)

• K-factor – Ratio between DHV and AADT

DHV K AADT

Traffic Parameters • In high volume roads, AADT is not used. Instead, the Design Hourly Volume (DHV) is used to avoid problems of congestion and determine acceptable levels of service. • DHV = 30th highest hourly volume in a year. In Spanish, Volumen Horario de Diseño (DHV)

DHV K AADT • k = traffic percentage in the design hour (highest hourly factor) • PHF = Peak Hour Factor in one hour (15 minute period)

Traffic Parameters

Hourly Volume

30th Highest Volume k AADT If there is not enough information, a value of k = 10% is recommended

1st

30th

Annual Hourly Ranking

8760

Typical Graph

Traffic Parameters • Directional distribution factor (D) ✓ Factor reflecting the proportion of peak-hour traffic traveling in the peak direction ✓ Often there is much more traffic in one direction than the other.

• Directional design-hour volume (DDHV) DDHV = K ×D× AADT

Example

TIME

VEHICLE COUNTS

700 – 715

400

715 – 730

500

730 – 745

700

745 – 800

900

800 – 815

800

815 – 830

800

830 – 845

500

845 – 900

200

Determine the peak hour factor

Example

Assume that the 3-lane avenue capacity is 200 vehicles per lane in 15 minutes. Determine the peak hour factor and the relationship between volume and capacity (v/c). What this value means?

TIME

VEHICLE COUNTS

700 – 715

400

715 – 730

500

730 – 745

700

745 – 800

900

800 – 815

800

815 – 830

800

830 – 845

500

845 – 900

200

Example

Assume that the 3-lane avenue capacity is 200 vehicles in 15 minutes or 800 vehicles in one hour per lane. How can you estimate the DHV ?

TIME

VEHICLE COUNTS

700 – 715

400

715 – 730

500

730 – 745

700

745 – 800

900

800 – 815

800

815 – 830

800

830 – 845

500

845 – 900

200

Traffic Parameters Hourly Factor In the previous example, not all the hours were available. In such scenario, one or more hours can be used and adding its HF, the daily volume can be calculated.

Hourly Volume   HourlyFactor  DailyVolume

Example 02

Traffic Parameters • Growth Factors It can be estimated based on a • Lineal function • Exponential function

Relationship.. or can be computed based on economical and social variables such as : • Population • Vehicle ownership

Traffic Parameters • Growth Factor • GFlineal = (1 + n.G) • GFexponential = (1 + G)n • GFpopulation = Popfut / Popcurrent where • G = annual growth rate • n = number of years

Exercises

Traffic Parameters • EXERCISE 01: • • • •

Current Year: 2012 Design Year: 2030 DHV2012 = 5,000 vph Annual Growth Rate = 4%

• Determine DHV2030

Traffic Parameters EXERCISE 02: • Current Population (2012) = 170,000 • Expected Population (2030) = 300,000

• If the current DHV is 5,000 vehicles • Calculate the DHV in 2030

Exercise 03

If AADT is 3500 vpd and the 30th highest hourly volume for the year is 420 vph, what is the K-factor for that facility?

Question: What’s the impact of choosing different K factor for design?

If AADT is 3500 vpd, how will the design volume differ for k-factor = 8% vs. 12%?

Exercise 04

If traffic is directionally split 60/40, what is directional distribution of traffic for previous example (Design hourly volume = 420 veh/hr)?

T-factor • • • •

T = percentage of heavy vehicles during design hour Affects capacity, ability to pass on two-lane rural roads, etc. Larger, occupy more space Should determine % during design hour (truck patterns may not be same as passenger vehicles)

Exercise 05 • Consider a rural highway with a projected 20-year AADT of 40,000 vpd. For the type of highway and region in question, it is known that peak-hour traffic currently is approximately 20% of the AADT, and that the peak direction generally carries 65% of the peak-hour traffic. What is the DDHV?

Exercise 06 Table below shows AADT from the last 3 years. Estimate the AADT for the year 2020.

Year

AADT

2013

12080

2014

12240

2015

12400

Dr. Alex M. Sanchez

Dr. Alex M. Sanchez

Dr. Alex M. Sanchez

Calculate the AADT for an intersection

Dr. Alex M. Sanchez

Calculate the AADT for an intersection

Dr. Alex M. Sanchez

Dr. Alex M. Sanchez

Traffic Parameters Some typical data: • Street Typical Capacity: 8000 vplpd • Freeway Typical Capacity: 2000 vplph

For some type of roads: • Residential

500 to 5000 vplpd

• Collector

5000 to 15000 vplpd

• Arterial

15000 to 50000 vplpd

• Highways / Freeways

More than 50000 vplpd

CONCLUSIONES 01

Collecting traffic data is the most important task in transportation analysis. It is important to determine current and future demand conditions.

02

There are diverse methods for collecting traffic data, conventional ones like manual counts and modern methods, which use the technology.

03

In order to carry out adequate traffic studies, it is necessary to know different terms that will lead us to determine the state of the roadway. Some of these concepts are: AADT, ADT, DHV, DDHV, etc. All of them will be cover in the next class sessions.

REFERENCIAS

▪ Garber and Hoel (2008). Traffic and Highway Engineering, 4th Edition.