fig1 illustrates a reed vehicle speed sensor 10 mounted on the output shaft 3 of an automatic transmission of a vehicle . as shown in fig1 the reed vehicle speed sensor 10 includes an annular member 1 having a plurality of vanes 5 projecting in a radial direction therefrom . the annular member 1 is mounted on the output shaft 3 of the automatic transmission such that as the output shaft 3 rotates , the annular member 1 also rotates . the reed vehicle speed sensor 10 further includes a magnetic sensor 7 which detects when a vane 5 passes the magnetic sensor 7 . typically , reed vehicle speed sensors have vanes symmetrically arranged about the circumference of the annular member . the reed vehicle speed sensor 10 of the present invention , however , has the vanes 5 asymmetrically arranged about the circumference of the annular member 1 . consequently , the reed vehicle speed sensor 10 will generate a different output waveform when the output shaft 3 rotates in direction a ( as indicated by the arrow in fig1 ), than when rotating in direction b ( as indicated by the arrow in fig1 ). fig2 ( a ) illustrates the output waveform of the reed vehicle speed sensor 10 when the reed vehicle speed sensor 10 rotates in direction a , while fig2 ( b ) illustrates the output waveform of the reed vehicle speed sensor 10 when the reed vehicle speed sensors 10 rotates in direction b . as shown in fig2 ( a ) and 2 ( b ), the reed vehicle speed sensor 10 outputs pulses as the vanes 5 pass the magnetic sensor 7 . the time periods t1 , t2 , t3 , . . . , tn between pulses differ when the reed vehicle speed sensor 10 rotates in directions a and b . by measuring the time periods between the pulses in the output waveform from the reed vehicle speed sensor 10 , the rotation direction of the output shaft 3 can be determined using the table illustrated in fig3 . consequently , once mounted on a vehicle , the rotation directions a and b will correlate to the vehicle traveling in either the forward direction or the backward direction such that by using the relationship illustrated in fig3 the direction in which the vehicle is traveling can be determined . fig4 illustrates the apparatus for controlling an automatic transmission in the absence of a driving mode signal from the driving mode sensor of a vehicle according to the present invention . as shown in fig4 the apparatus includes a transmission control unit ( tcu ) 2 connected to the reed vehicle speed sensor 10 and a driving mode sensor 20 . of course , it will be understood by those skilled in the art , that the tcu 2 also receives the output from a plurality of other sensors , but those sensors have not been illustrated for clarity . the tcu 2 includes a cpu 4 connected to a rom 8 and a ram 6 . the rom 8 stores programs which the cpu 4 runs when controlling an automatic transmission . the ram 6 stores output received from the various sensors connected to the tcu 2 , and intermediate values calculated during the running of the program stored by the rom 8 . based on the programs stored in the rom 8 , the cpu 4 generates control signals for the automatic transmission . either the rom 8 or the ram 6 also store various tables , etc . used by the cpu 4 in generating the control signals . fig5 illustrates the flow chart for the method of controlling an automatic transmission in the absence of a driving mode signal from the driving mode sensor of a vehicle according to the present invention . the program implementing this method is stored in the rom 8 and run by the cpu 4 of the tcu 2 . when the vehicle including the tcu 2 is started , power is supplied to the tcu 2 to &# 34 ; start up &# 34 ; the tcu 2 in step s10 . the tcu 2 then receives a signal from the driving mode sensor 20 in step s12 . next , in step s14 , the tcu 2 determines whether or not a driving mode signal was received . if a driving mode signal was received , then processing proceeds to step s34 where the tcu 2 controls the automatic transmission according to any well - known technique based on the driving mode signal . if , however , in step s14 , the tcu 2 determines that it did not receive a driving mode signal , then processing proceeds to step s16 . in step s16 , the tcu 2 generates and outputs control signals to the automatic transmission to place the automatic transmission in first gear . then , in step s18 , the tcu 2 detects the driving direction of the vehicle . specifically , the tcu 2 receives the output signals of the reed vehicle speed sensor 10 . using the table of fig3 stored in the rom 8 or the ram 6 , the tcu 2 determines whether the output waveform from the reed vehicle speed sensor 10 matches the output waveform corresponding to the backward direction of vehicle travel . if the output waveforms match , then the tcu 2 determines that the vehicle is traveling backwards , and in step s28 generates and outputs control signals to the automatic transmission to place the automatic transmission in reverse . if , however , in step s20 , the tcu 2 does not determine that the vehicle is traveling backwards , then in step s22 the tcu 2 determines whether the vehicle is traveling forward . again , the tcu 2 compares the output waveform of the reed vehicle speed sensor 10 to the output waveform stored in the table of fig3 corresponding to vehicle travel in the forward direction . if a match is found , then the tcu 2 determines that the vehicle is traveling in the forward direction , and generates and outputs control signals to the automatic transmission in step s26 to place the automatic transmission in drive . if , however , in step s22 the tcu 2 does not determine that the vehicle is driving in the forward direction , then in step s24 the tcu 2 selects the neutral driving mode , and outputs control signals to the automatic transmission accordingly . after steps s24 , s26 , or s28 , processing proceeds to step s30 . in step s30 , the tcu 2 delays further processing for a predetermined period of time . in a preferred embodiment , the predetermined period of time is 0 . 5 seconds . this allows the control determined in either step s24 , s26 , or s28 to continue for at least 0 . 5 seconds . after step s30 , processing proceeds to step s31 wherein the tcu 2 again receives a signal from the driving mode sensor 20 . next , in step s32 , the tcu 2 determines whether a driving mode signal was received . if no driving mode signal was received , processing returns to step s18 . if , however , a driving mode signal was received , then processing proceeds to step s34 discussed above . as discussed above , when a vehicle is initially started and no driving mode signal is received by the transmission control unit , conventional transmission control units place the vehicle in neutral . consequently , when the driver depresses the accelerator pedal , the engine revs , causing discomfort to the driver . by contrast , under the same conditions , the transmission control unit according to the present invention determines whether to select one of the reverse , drive , or neutral driving mode . thus , if the driver does move the driving mode select lever to drive or reverse and the vehicle begins to drift forward or backwards , respectively , the tcu according to the present invention will select the drive or reverse driving mode such that power is transmitted from the engine to the driving wheels of the vehicle . as a result , the engine does not rev and the driver is not disconcerted . the invention being thus described , it will be obvious that the same may be varied in many ways . such variations are not to be regarded as a departure from the spirit and scope of the invention , and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims .