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Page 384
Suggested Citation:"Appendix G: Glossary." National Academies of Sciences, Engineering, and Medicine. 2020. Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets. Washington, DC: The National Academies Press. doi: 10.17226/25963.
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Suggested Citation:"Appendix G: Glossary." National Academies of Sciences, Engineering, and Medicine. 2020. Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets. Washington, DC: The National Academies Press. doi: 10.17226/25963.
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Suggested Citation:"Appendix G: Glossary." National Academies of Sciences, Engineering, and Medicine. 2020. Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets. Washington, DC: The National Academies Press. doi: 10.17226/25963.
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Suggested Citation:"Appendix G: Glossary." National Academies of Sciences, Engineering, and Medicine. 2020. Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets. Washington, DC: The National Academies Press. doi: 10.17226/25963.
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Suggested Citation:"Appendix G: Glossary." National Academies of Sciences, Engineering, and Medicine. 2020. Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets. Washington, DC: The National Academies Press. doi: 10.17226/25963.
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Suggested Citation:"Appendix G: Glossary." National Academies of Sciences, Engineering, and Medicine. 2020. Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets. Washington, DC: The National Academies Press. doi: 10.17226/25963.
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378 A P P E N D I X G Glossary General Acronyms 𝐴𝑇𝐷𝑀 = Active Traffic and Demand Management; 𝐴𝑊𝑆𝐶 = all-way stop controlled intersection; 𝐷𝐷𝐼 = diverging diamond interchange; 𝐷𝑂𝑇 = Department of Transportation; 𝐸𝐵 = eastbound; 𝐹𝐻𝑊𝐴 = Federal Highway Administration; 𝐻𝐶𝑀 = Highway Capacity Manual; 𝐼𝐶𝑀 = Integrated Corridor Management; 𝐼𝑅𝑇 = interchange ramp terminal; 𝑀𝑂𝐸 = Measures of Effectiveness; 𝑁𝐵 = northbound; 𝑄𝐴𝑃 = queue accumulation polygon; 𝑆𝐵 = southbound; 𝑆𝑃𝑈𝐼 = single-point urban interchange; 𝑇𝑊𝑆𝐶 = two-way stop controlled intersection; 𝑊𝐵 = westbound. General Values 𝑑/𝑐 = demand to capacity ratio; 𝐸𝐷 = expected demand (veh/h); 𝑓 = adjustment factor for heavy vehicle presence; 𝐹𝐹𝑆 = free flow speed (mi/h); 𝐺 = grade (%); 𝐿𝑂𝑆 = level of service; 𝑂 − 𝐷 = origin-destination; 𝑃𝐻𝐹 = peak hour factor; 𝑃𝑀𝑇 = personal miles traveled (mi); 𝑣/𝑐 = volume/capacity ratio 𝑉𝑀𝑇 = vehicle miles traveled (mi).

379 1. Arterial Facilities 1.1. General concepts 𝑐 = merging capacity at the freeway (veh/h); 𝑐 = capacity of ramp proper (pc/h) (Eq. 38-2); capacity of the off-ramp roadway (pc/h) (Eq. 38-A1, 38-A3, 38-A6); 𝐿 = average vehicle spacing in stationary queue (ft/veh); 𝜆 = departure rate from the major-street left-turn into the on-ramp (veh/h); 𝜆 = total on-ramp demand throughput (pc/h); 𝜆 = departure rate from major street right turn into the on-ramp (veh/h); 𝜆 = departure rate from the minor street through into the on-ramp (veh/h); 𝑄 ,( ) = 95th percentile of queue, where (a) = approach direction (veh); 𝑠 = saturation flow rate of movement 𝑖 (veh/h/ln); 𝑣 = maximum entering flow rate for the intersection approach (veh/h); 𝑥( ) = volume-to-capacity ratio for approach direction a 1.2. Signalized Intersections 𝑐 = capacity for approach 𝑖 (veh/h); 𝑔 = green extension time (s); 𝑔 = green service time (s); 𝑙 = start-up lost time (s); 𝑙 = clearance lost time (s); 𝑁 , = total number of vehicles discharged from each protected movement 𝑖; 𝑁 , = total number of vehicles discharged from each permitted movement 𝑖; 𝑁 , , = total number of vehicles discharged for movement 𝑖 during the green extension time; 𝑁 , , = total number of vehicles discharged for movement 𝑖 during the queue service time; 𝑞 = arrival flow rate during the effective green time = 𝑃 𝑞 𝐶/𝑔 (veh/s); 𝑟 = effective red time (s); 𝑅 = platoon ratio; 𝑋 = demand-to-capacity ratio for spillback conditions. 1.3. TWSC Intersections cm,j = movement capacity for movement i (Equations 20-36, 20-37 and 20-40). cSB,i = capacity during spillback for movement i (veh/h) cEQ,i = adjusted capacity for movement i (veh/h) N(t) = number of queued vehicles along the on-ramp at time t; T = duration of analysis time period (minutes)

380 TSB = time period with active spillback (minutes) 1.4. AWSC Intersections 𝑐 , = potential capacity for the minor street through (veh/h); cSB,i = capacity during spillback for movement i (veh/h) cEQ,i = adjusted capacity for movement i (veh/h) N(t) = number of queued vehicles along the on-ramp at time t; T = duration of analysis time period (minutes) TSB = time period with active spillback (minutes) ℎ = departure headway during queue spillback (s/veh); 1.5. Roundabouts 𝜆( ), = maximum throughput for (a) movement (pc/h); 𝑐 ,( ) = entry lane capacity for roundabout approach, where (a) = approach direction (pc/h); 𝑑( ) = average control delay for (a) approach (sec/veh); 𝑑 = additional delay due to on-ramp spillback (sec/veh); ℎ , = departure headway for the major street left turn (s); ℎ , = departure headway for the major street right turn (s); ℎ , = departure headway for the minor street through (s); ℎ = departure saturation headway into the on-ramp (s/veh); p(a)-ONR = percent of demand from NB approach a into the on-ramp 𝑄 = expected queue length QSP along the on-ramp during a 15-minute period analysis; 𝑄 = total number of vehicles queued during a 15-minute time period analysis; 𝑣( ), = flow rate for roundabout approach a (veh/h) 𝑣 ,( ), = circulating flow rate for roundabout approach a (veh/h) 𝑣 ,( ), = entry flow rate for roundabout approach a (veh/h) total number of vehicles queued during a 15-minute time period analysis 2. Freeway Facilities 2.1. Lane by lane analysis ∆𝑁𝑉(𝑖, 𝑡,𝑝)= additional density of segment 𝑖 at the end of time step 𝑡 during time interval 𝑝 (veh/mi/ln); 𝐿𝐹𝑅 = lane flow ratio; 𝑎 = empirical constant; 𝐵𝑃 = breakpoint value; 𝑐 = empirical constant; 𝐶𝐴𝐹 = capacity adjustment factor for the upstream freeway area; 𝑓 = adjustment factor for 𝑎; (Eq. 38-3, 38-C2, 38-C3, 38-C5, 38-C7)

381 𝑓 , = adjustment factor for 𝑎; due to impact of grade; 𝑓 , = adjustment factor for 𝑎; due to impact of interchange density; 𝑓 , = adjustment factor for 𝑎; for length of the weaving segment; 𝑓 , = adjustment factor for 𝑎; due to impact of access point density; 𝑓 , = adjustment factor for 𝑎; due to impact of trucks; 𝑓 , = adjustment factor for 𝑎; for off-ramp flow; 𝑓 , = adjustment factor for 𝑎; for on-ramp flow; 𝑓 , = adjustment factor for 𝑎; due to impact of ramp flow; 𝑓 , = adjustment factor for 𝑎; for volume ratio; 𝑓 = adjustment factor for 𝑐; (Eq. 38-3, 38-C2, 38-C4, 38-C6, 38-C8) 𝑓 , = adjustment factor for 𝑐; due to impact of grade; 𝑓 , = adjustment factor for 𝑐; due to impact of interchange density; 𝑓 , = adjustment factor for 𝑐; for length of the weaving segment; 𝑓 , = adjustment factor for 𝑐; due to impact of access point density; 𝑓 , = adjustment factor for 𝑐; due to impact of trucks; 𝑓 , = adjustment factor for off-ramp flow; 𝑓 , = adjustment factor for on-ramp flow; 𝑓 , = adjustment factor due to impact of ramp flow; 𝑓 , = adjustment factor for volume ratio; ℎ = reaction headway (s); 𝐼𝐷 = interchange density (veh/mi/ln); 𝐾𝐵 = background density (veh/mi/ln); 𝑛 = access point density – number of ramps half a mile upstream and half mile downstream (veh/mi/ln); 𝑡 = truck percentage (%); 𝑣 = segment entering demand (pc/h); 𝑣 = ramp flow for freeway analysis (veh/hr); 𝑣 , = off-ramp flow for freeway analysis (veh/hr); 𝑣 , = on-ramp flow for freeway analysis (veh/hr); and 𝑉𝑅 = volume ratio (weaving volume/total volume). 2.2. Off-ramp queue spillback 𝑐 = capacity of ramp proper (pc/h) (Eq. 38-2); capacity of the off-ramp roadway (pc/h) (Eq. 38-A1, 38-A3, 38-A6); 𝑓 = adjustment factor for driver population; 𝐾𝐵𝐵𝐿(𝑖, 𝑡,𝑝) = background density (pc/mi/ln) of the blocked portion of segment 𝑖 during time step 𝑡 in time interval 𝑝; 𝐾𝐵𝑈𝐵(𝑖, 𝑡,𝑝) = background density (pc/mi/ln) of the unblocked portion of segment 𝑖 during time step 𝑡 in time interval 𝑝; 𝐿 = section 𝑖 length (ft); 𝐿 (𝑖,𝑝) = available deceleration lane length (ft) for segment 𝑖 during time period 𝑝; 𝐿 , 𝐿 = available queue storage distance (ft/ln); 𝐿 = length of the weaving segment (ft);

382 𝐿𝐹𝑅 = share of the total flow on lane 𝑖 𝑂𝐹𝑅𝐹(𝑖, 𝑡,𝑝) = actual flow that can exit at off-ramp 𝑖 during time step 𝑡 in time interval 𝑝 (veh/h); 𝑂𝑁𝑅𝑂(𝑖, 𝑡,𝑝) = maximum output flow rate that can enter the merge point from on-ramp 𝑖 during time step 𝑡 in time interval 𝑝 (veh/h); 𝑂𝑁𝑅𝑄 = onramp queue length (veh); 𝑀𝐹𝐵𝐿(𝑖, 𝑡,𝑝) = mainline flow rate that can cross the blocked portion of node 𝑖 during time step 𝑡 in time interval 𝑝; 𝑀𝐹𝑈𝐵(𝑖, 𝑡,𝑝) = mainline flow rate that can cross the unblocked portion of node 𝑖 during time step 𝑡 in time interval 𝑝; 𝑀𝐼𝐵𝐿(𝑖, 𝑡,𝑝) = maximum flow desiring to enter the blocked portion of node 𝑖 during time step 𝑡 in time interval 𝑝; 𝑀𝐼𝑈𝐵(𝑖, 𝑡,𝑝) = maximum flow desiring to enter the unblocked portion of node 𝑖 during time step 𝑡 in time interval 𝑝; 𝑀𝑄1(𝑖, 𝑡,𝑝) = mainline queue length of off-ramp unserved vehicles in the rightmost mainline lane, for segment 𝑖 during time period p in time interval 𝑡; 𝑀𝑄2(𝑖, 𝑡,𝑝) = mainline queue length of off-ramp unserved vehicles in the rightmost mainline lane, for segment 𝑖 during time period p in time interval 𝑡; 𝑁 , = number of lanes in section 𝑖 that are associated to ramp lane 𝑘; 𝑁 = number of approaching lanes for lane group 𝑚; 𝑁𝑉 = number of vehicles (veh); 𝑁𝐸𝑋𝑇𝑂𝐹𝑅(𝑖) = index of the nearest downstream diverge segment relative to subject node 𝑖; 𝑂𝐹𝑅𝐷𝐼𝑆𝑇(𝑖) = distance (ft) from node 𝑖 to the start of the deceleration lane at the nearest downstream off-ramp; 𝑂𝐹𝑅𝐿𝑄(𝑖, 𝑡,𝑝) = queue length of off-ramp unserved vehicles for diverge segment 𝑖 during time period 𝑝 in time interval 𝑡; 𝑂𝐹𝑅𝐹𝑈𝑃(𝑖, 𝑡,𝑝) = flow that can exit at the closest off-ramp downstream of 𝑖 during time step 𝑡 in time interval 𝑝; 𝑂𝐹𝑅𝑈𝑉(𝑖, 𝑡,𝑝) = number of off-ramp unserved vehicles for segment 𝑖 during time period p in time interval 𝑡; 𝑄 = queue growth during analysis period 𝑖 (pc); 𝑄𝐼𝐴(𝑖,𝑝) = length of the queue influence area (ft) for segment 𝑖 during time period 𝑝 (ft); 𝑄 , = number of queued vehicles in Ramp Lane 𝑘, during a 15-min interval (pc); 𝑄 , = number of queued vehicles from Lane Group 𝑚 associated with ramp lane 𝑘, during a 15-min interval (pc); 𝑄 = maximum queue length on the ramp (pc); 𝑄 %, = estimated back of queue length (nth percentile), as defined in Equation 31-150 (veh/ln); 𝑄 = length of queue beyond ramp storage distance (ft); 𝑄 = queue length during for the analysis period 𝑡 (pc); 𝑅 = on-ramp storage ratio (veh); 𝑅𝐶(𝑖,𝑝)= Capacity of the ramp proper (pc/h) during time period 𝑝 in time interval 𝑡; 𝑅𝐹(𝑖, 𝑡,𝑝) = flow (pc/ts) that can enter the ramp proper at segment 𝑖 during time period p in time interval 𝑡; 𝑅𝐼(𝑖, 𝑡,𝑝) = maximum flow (pc/ts) desiring to enter the off-ramp on segment 𝑖 during time period 𝑝 in time interval 𝑡; 𝑅𝐾𝐵(𝐼, 𝑡,𝑝) = ramp proper queue density (pc/mi/ln) for segment 𝑖 during time period p in time interval 𝑡; 𝑅𝐾𝐶 = ramp density at capacity (pc/mi/ln); 𝑅𝐿(𝑖) = length of ramp proper (ft) for segment 𝑖; 𝑅𝑀(𝑖, 𝑡, 𝑝) = metering rate at on-ramp 𝑖 during time step 𝑡 in time interval 𝑝 (veh/h); 𝑅𝑁(𝑖) = number of ramp lanes for segment 𝑖; 𝑅𝑁𝑉(𝑖, 𝑡,𝑝) = maximum number of vehicles (pc) within the ramp of segment 𝑖 at the end of time step 𝑡 during time interval 𝑝; 𝑅𝑈𝑉(𝑖, 𝑡,𝑝) = number of unserved vehicles at the entrance of the ramp proper of segment 𝑖 at the end of time step 𝑡

383 during time interval 𝑝; 𝑆 = number of computational time steps in an analysis period; 𝑠 = measured speed at the beginning of congestion at the upstream detector (mi/h) 𝑆𝐵𝐾𝑄 (𝑖, 𝑡,𝑝) = spillback queue density for segment 𝑖 during time period 𝑝 in time interval 𝑡; 𝑆𝐵 (𝑖, 𝑡,𝑝) = capacity adjustment when one or more lanes of segment 𝑖 are entirely blocked during time period 𝑝 in time interval 𝑡; 𝑆𝐵 (𝑖, 𝑡,𝑝) = capacity adjustment factor for approaching vehicles within the queue influence area upstream of an off- ramp queue; 𝑆𝐵𝐿𝐶(𝐼, 𝑡,𝑝) = number of lane change maneuvers within the Queue Influence Area at node 𝐼, during time step 𝑡 in time interval 𝑝; 𝑆𝐵𝐿𝑄(𝑖, 𝑡,𝑝) = queue length within segment 𝑖 during time period 𝑝 in time interval 𝑡; 𝑆𝐿(𝑖,𝑝) = available shoulder length (ft) for segment 𝑖 during time period 𝑝; 𝑇𝐼𝐴 = total influence area (ft); 𝑣 = on-ramp flow rate (veh/h) (Eq. 38-B10); off‐ramp demand for the period (pc/h) (Eq. 38-A1, 38-A3, 38- A6);

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The procedures detailed in the 6th Edition of the Highway Capacity Manual (HCM) estimate capacity and several operational measures, including those determining Level of Service, for freeway facilities as well as surface streets.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 290: Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets introduces materials to help modify the freeway analysis methods and the urban street methods so that the effects of operations from one facility to the other can be evaluated.

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