Download Record of Activities, Problems, Issues, Success - Lecture Notes | CE 474 and more Study notes Civil Engineering in PDF only on Docsity! Class 05 – Traffic Systems Design 8 September 2008 1 CLASS PLAN AND RECORD Class/Date: Class 06 (8 September 2008) Plan (Topics to Cover): Record of Activities, Problems, Issues, Success: Class 05 – Traffic Systems Design 8 September 2008 2 Slide Notes 1 Welcome to Class 05. 2 Outline of topics to cover today. 3 Web site of the day. 4 Quiz. I give reading assignments ahead of time, and I give you study questions so that you can focus on the important points that we will cover and discuss in the following class period. These are not optional readings; they are given with the expectation that you will read the material and that you will be ready to discuss it. Today we will have a short quiz that covers some of what we discussed last week and some of the reading for today. Please take out a blank sheet of paper and be ready to answer these questions individually. 1. If you were designing this intersection with a goal of achieving LOS D, would you be satisfied or not? 2. Why is the uniform delay term not adequate to represent the performance of this intersection? 5 3. Write the degree of saturation in a form that includes the green time. [Hint: X = v/c] 6 4. What is a ring? 7 5. What is a ring diagram? 8 What is phasing? From the perspective of the HCM, it is the part of the signal cycle allocated to any combination of traffic movements receiving the right of way simultaneously during one or more intervals. [see screen shot on slide] Why is this different from the “phase” definitions we will use? • In the HCM, we assume a fixed set of intervals that always come in the same sequence, that represent one cycle that is representative of the intersection that we are studying. • In reality, green time that we observe is the result of a complex interaction of timing processes in the traffic controller, and the users that are detected by the traffic control system. Class 05 – Traffic Systems Design 8 September 2008 5 Slide Notes Add text on precedence graphs and examples of critical path through the timing network. 12 In lab tomorrow, you will learn how to use a microsimulation model. This slide (which we’ve seen before) shows a classification of models. A microsimulation model includes the following characteristics: • We consider the behavior of individual behavior reacting either to drivers in front of them or the signal display status. • Driver behavior is stochastic: drivers behave differently and the same driver may behave differently at another time. • The model keeps track of vehicles and processes at very small time steps (here, 0.1 second). • The model can consider a large arterial or network of streets and intersections. • The model can consider both fixed time and actuated traffic control systems. • The model simulates a given set of conditions and does not usually find the optimal solution to your design problem. • The model can consider both oversaturated (congested) conditions as well as undersaturated conditions. This contrasts with the HCM: • We consider macroscopic flow. • Driver behavior is deterministic. • Large time slices are used, usually 15 minutes. • Single intersections are modeled with little or no interaction between adjacent intersections. • The model is based on fixed time traffic control, though it provides an approximation of actuated traffic control systems. • The model can both simulate and optimize. • The model is better when conditions are undersaturated. Class 05 – Traffic Systems Design 8 September 2008 6 Slide Notes 13 You have to walk before you can run, and the process of constructing a microsimulation model is not easy. Students often react to the length of time that it takes to construct the model, the ease of making mistakes and misunderstanding the rules that a given model imposes, and the challenge in calibrating a model to the particular conditions that you will be studying. Know this before you begin! Simulation is a powerful tool, but it is only a tool. With that being said, here is where you can go with a simulation model. This is a model of downtown Moscow that students constructed in this class using the VISSIM model. It is an “avi” file produced by the VISSIM model. [see handwritten notes]