Background technique
Journey time reflects the Trip Costs from starting point to destination, due to exophytic demand and supply factor and
It interacts between endogenous Driver's Factors, traveler is caused to generate random fluctuation in the journey time in path.In road network
Path forms time change there is time variation, randomness and uncertainty, and show complicated wave characteristic.Existing
In numerous studies, establish the prediction model of journey time using mathematical statistics method, main method include: history averaging model,
Linear regression model (LRM), time series models, Kalman filter model, Markov prediction, Maximum-likelihood estimation model etc..
However, traffic system is the random process for obeying certain probability distribution, the fluctuation of journey time is then this random data
The uncertainty of the realization traffic system of generating process, so that the time series of path forms time change is advised in numerical value change
There are some unique features in rule, be mainly shown as that the heteroscedasticity heteroscedasticity of journey time variation violates linear return
Return model about homoscedasticity it is assumed that but also conventional Time series analysis method (such as arma modeling) is no longer applicable in,
The parameter Estimation amount that model obtains is no longer valid, and the Forecasting of Travel Time value obtained based on model can also generate deviation.
Travel Time Reliability refers to that under a certain road, traffic, environment, traveler is in certain a road section, OD pairs of stroke
Between be no more than specified time probability, describe the degree of journey time variability.Relative to average travel time, journey time
Reliability index reflects the randomness and fluctuation of section or road network operating status comprehensively.Because average travel time characterizes sample
This intensity, but has ignored the details and variation range of journey time, cannot comprehensively embody the change of Link Travel Time
Change the stable state in section and traffic circulation.
The present invention is based on the characteristics such as the spike thickness tail of path forms time fluctuation, sociability, are introduced into econometrics
Stochastic Volatility Model (Stochastic Volatility Model, SV) and its extension form, using model parameter from different
The reliability of path journey time is analyzed and evaluated in angle.By model, both to path journey time fluctuation time variation,
Duration is evaluated, and also the distribution of exterior information is described, and outside is believed in the fluctuation of analysis path journey time
Cease the reaction mechanism of impact.To realize the overall evaluation to path Travel Time Reliability.Compared to ARCH model cluster
(Autoregressive Conditional Heteroskedasticity Model, autoregressive conditional different Variance model), SV
Class model describes the time-varying fluctuation of variance using unobservable random process, can be more accurate when comprehensively portraying stroke
Between sequence fluctuation characteristic.
As the pith of traffic behavior evaluation, Travel Time Reliability is evaluated for urban traffic control person,
They are essential decision factors, and traffic congestion, planning of science activities road network are alleviated in help.In addition Travel Time Reliability can also
For traveler path planning, to improve trip quality, optimization route line decision provides information reference.
Summary of the invention
The path forms time reliability analysis method based on Stochastic Volatility Model that the invention proposes a kind of, with realization pair
Path forms time reliability carries out more comprehensive assay.Not only enable manager is more efficiently to manage and control road
The operating status of net, and necessary trip information reference can be provided for traveler.
The purpose of the present invention is what is be achieved through the following technical solutions: the path forms time reliability based on random fluctuation
Analysis method, it is as follows that the method comprising the steps of:
A kind of path forms time reliability analysis method based on Stochastic Volatility Model, which is characterized in that include with
Lower step:
(1) by the floating car data information obtained, the data information in each path is extracted;Each path is calculated in difference
The journey time of period.Path forms time calculation method are as follows:
In formula, ti(t) indicate path i in the path forms time of t moment;IiIndicate the section set of composition path i, lj
Indicate the length of section j, vj(t) the road-section average travel speed of section j is indicated.
(2) exceptional value and missing values processing, and successively sequence obtains path row sequentially in time with 5min time interval
The time series of journey time.
(3) stability bandwidth of journey time is calculated, and statistics is described to stability bandwidth sequence.Path forms time fluctuation rate
Method are as follows:
Vt=(lnTt-lnTt-1)×100
Wherein, TtFor in the path forms time of t moment.
(4) Stochastic Volatility Model in each path is established.
Essentially random volatility model is as follows:
Vt=exp (ht/2)εt
According to the journey time stability bandwidth sequence in each path establish Forecast Means, thickness tail SV model, mean value SV model with
And lever SV model, estimated using parameter of the WinBUGS software to each equation.
(5) overall evaluation is fluctuated to path journey time.The whole fluctuation of path forms time can be by the time variation that fluctuates
It is evaluated, i.e., is reflected by the heteroscedasticity of journey time stability bandwidth series error item.In addition journey time stability bandwidth
Spike Boea crassifolia, concentration, duration etc. can also carry out quantitative analysis by the estimation of model parameter.To obtain to path row
The fail-safe analysis of journey time.
The invention has the benefit that being introduced into the Stochastic Volatility Model of financial field to the reliable of path journey time
Property evaluation in, the fluctuation characteristic of journey time is accurately comprehensively obtained by the parameter Estimation of SV model, providing journey time can
By the analysis method of property, reference is provided for the evaluation of the traffic reliability in region and city, and provide better trip for traveler
Planning guidance.
Specific embodiment
The present invention provides a kind of path forms time reliability analysis method based on Stochastic Volatility Model, below with reference to attached
The present invention will be described in detail for figure, as shown in Figure 1, the specific steps of the present invention are as follows:
Step 1: by the floating car data information of acquisition, the data information in each path is extracted;Each path is calculated to exist
The journey time of different periods and matching road section length.Path forms time calculation method are as follows:
In formula, ti(t) indicate path i in the path forms time of t moment;IiIndicate the section set of composition path i, lj
Indicate the length of section j, vj(t) the road-section average travel speed of section j is indicated.
Step 2: exceptional value and missing values processing, and successively sequence obtains road sequentially in time with 5min time interval
The time series of diameter journey time, the average value polishing of the missing values journey time of surrounding time point.
Step 3: journey time sequence itself is a non-stable time series, and still, correlative study shows right
After journey time sequence carries out logarithmetics processing, obtained time series is the whole sequence of a single order list that is, logarithm
Change treated journey time sequence, first-order difference sequence is a stable time series.It is counted using the sequence
Analysis, can eliminate the heteroscedasticity of stochastic error in regression model, reduce the interference of uncertain factor, to guarantee to divide
Analysing result has good statistical property.
With reference to the definition in economics to earning rate etc., the first-order difference of journey time logarithm is defined as journey time
Stability bandwidth, i.e.,
Vt=(lnTt-lnTt-1)×100
Wherein, TtFor in the path forms time of t moment.
Step 4: journey time wave characteristic is divided according to obtained journey time stability bandwidth time series track
Analysis calculates the preliminary analysis that mean value, standard deviation, the degree of bias, kurtosis, JB statistic etc. carry out fluctuation.
Standard deviation
The degree of bias
Kurtosis
Jarque-Beta statistic
Wherein, n is sample size, and k is freedom degree.In each statistic, Jarque-Bera statistic is for examining one group
Can sample think the statistic from normal distribution totality.
Step 5: the Stochastic Volatility Model in each path is established.
(1) SV-N model
Taylor (1986) proposes standard SV model in the autoregression behavior for explaining financial income sequence volatility model, letter
Referred to as SV-N model, form are as follows:
yt=exp (θt/2)εt,εt~i.i.d N (0,1) t=1,2 ..., n
θt=μ+φ (θt-1-μ)+ηt,ηt~i.i.d N (0, τ2), t=1,2 ..., n
Wherein ytIndicate t days journey time stability bandwidths, εtFor independent identically distributed white noise acoustic jamming, obeying mean value is
0, the normal distribution that variance is 1;ηtHorizontal for the disturbance of independent identically distributed fluctuation, obeying mean value is 0, variance τ2Normal state
Distribution.Error term ηtWith εtIt is incoherent, is all unobservable.φ is persistence parameter, reflects current fluctuation to future
The influence of fluctuation, and for | φ | < 1, SV model are covariance stationaries.Potential fluctuation θtObey a duration ginseng
Number is Gauss AR (1) process of φ.
(2) SV-T model
SV-T model is a kind of thick tail SV model, has the ability for the spike rear molding for capturing journey time sequence.In SV-T
In model, ε is disturbedtThe t that freedom degree is ω is obeyed to be distributed:
yt=exp (θt/2)εt,εt~i.i.d t (0,1, ω)
θt=μ+φ (θt-1-μ)+ηt,ηt~i.i.d N (0, τ2), t=1,2 ..., n
(3) SV-MN model
It is generalized in SV model by the ARCH-M model that Engle, Lilien and Robins are proposed by Koopman (2002),
Propose SV-M model.Risk compensation is considered in SV-M model.The form of SV-MN model based on normal distribution is as follows:
yt=dexp (θt)+εtexp(θt/2),εt~i.i.d N (0,1) t=1,2 ..., n
θt=μ+φ (θt-1-μ)+ηt,ηt~i.i.d N (0, τ2) t=1,2 ..., n
Wherein dexp (θt) it is risk compensation, d refers to the regression coefficient of measurement mean value fluctuation effect.θtObedience mean value be μ+
φ(θt-1- μ), variance τ2Normal distribution, i.e. θt|μ,φ,θt-1~N (μ+φ (θt-1-μ),τ2)。
(4) Leverage SV model
If journey time changes same magnitude upward or downward, its fluctuation during slide downward wants high
Fluctuation in moving upwards, is referred to as leverage.It is compared with Forecast Means, leverage SV (Leverage SV)
Model has an additional parameter, is exactly correlation coefficient ρ.
yt|θt, ρ=exp (θt/2)εtεt~i.i.d tkT=1,2 ..., n
θt+1|θt,μ,φ,τ2, ρ=μ+φ (θt-μ)+τηtηt~i.i.d N (0, τ2) t=1,2 ..., n-1
According to the journey time stability bandwidth sequence in each path establish Forecast Means, thickness tail SV model, mean value SV model with
And the SV model containing external factor, estimated using parameter of the WinBUGS software to each equation.
By taking SV-N model as an example, code is as shown in figure 3, output parameter is respectively mu, phi, tau.Mu is used to investigate wave
Dynamic mean value is horizontal, and phi is used to investigate the duration of fluctuation, and the disturbance that tau is used to investigate fluctuation is horizontal.
Step 6: the overall evaluation is fluctuated to path journey time.The whole fluctuation of path forms time can by fluctuate when
Denaturation is evaluated, i.e., is reflected by the heteroscedasticity of journey time stability bandwidth series error item.In addition journey time fluctuates
The spike Boea crassifolia of rate, concentration, duration etc. can also pass through the estimation of model parameter and carry out quantitative analysis.To be satisfied the need
The fail-safe analysis of diameter journey time.
The technical concepts and features of above embodiment only to illustrate the invention, its object is to allow be familiar with technique
People can understand the contents of the present invention and be implemented, and it is not intended to limit the scope of the present invention, it is all according to the present invention
Equivalent change or modification made by Spirit Essence, should be covered by the scope of protection of the present invention.